Integrated circuit including cross-coupled transistors having gate electrodes formed within gate level feature layout channels with shared diffusion regions on opposite sides of two-transistor-forming gate level feature

ABSTRACT

A semiconductor device includes conductive features within a gate electrode level region that are each fabricated from a respective originating rectangular-shaped layout feature having a centerline aligned parallel to a first direction. The conductive features form gate electrodes of first and second PMOS transistor devices, and first and second NMOS transistor devices. The gate electrodes of the first PMOS and first NMOS transistor devices extend along a first gate electrode track. The gate electrodes of the second PMOS and second NMOS transistor devices extend along a second gate electrode track. A first set of interconnected conductors electrically connect the gate electrodes of the first PMOS and second NMOS transistor devices. A second set of interconnected conductors electrically connect the gate electrodes of the second PMOS and first NMOS transistor devices. The first and second sets of interconnected conductors traverse across each other within different levels of the semiconductor device.

CLAIM OF PRIORITY

This application is a continuation application under 35 U.S.C. 120 ofprior U.S. application Ser. No. 12/753,798, filed Apr. 2, 2010, which isa continuation application under 35 U.S.C. 120 of prior U.S. applicationSer. No. 12/402,465, filed Mar. 11, 2009, issued as U.S. Pat. No.7,956,421, which claims priority under 35 U.S.C. 119(e) to each of 1)U.S. Provisional Patent Application No. 61/036,460, filed Mar. 13, 2008,2) U.S. Provisional Patent Application No. 61/042,709, filed Apr. 4,2008, 3) U.S. Provisional Patent Application No. 61/045,953, filed Apr.17, 2008, and 4) U.S. Provisional Patent Application No. 61/050,136,filed May 2, 2008. The disclosure of each above-identified patentapplication is incorporated in its entirety herein by reference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to each application identified in the tablebelow. The disclosure of each application identified in the table belowis incorporated herein by reference in its entirety.

Filing Application No. Date 12/753,711 Apr. 2, 2010 12/753,727 Apr. 2,2010 12/753,733 Apr. 2, 2010 12/753,740 Apr. 2, 2010 12/753,753 Apr. 2,2010 12/753,758 Apr. 2, 2010 12/753,766 Apr. 2, 2010 12/753,776 Apr. 2,2010 12/753,789 Apr. 2, 2010 12/753,793 Apr. 2, 2010 12/753,795 Apr. 2,2010 12/753,805 Apr. 2, 2010 12/753,810 Apr. 2, 2010 12/753,817 Apr. 2,2010 12/754,050 Apr. 5, 2010 12/754,061 Apr. 5, 2010 12/754,078 Apr. 5,2010 12/754,091 Apr. 5, 2010 12/754,103 Apr. 5, 2010 12/754,114 Apr. 5,2010 12/754,129 Apr. 5, 2010 12/754,147 Apr. 5, 2010 12/754,168 Apr. 5,2010 12/754,215 Apr. 5, 2010 12/754,233 Apr. 5, 2010 12/754,351 Apr. 5,2010 12/754,384 Apr. 5, 2010 12/754,563 Apr. 5, 2010 12/754,566 Apr. 5,2010

BACKGROUND

A push for higher performance and smaller die size drives thesemiconductor industry to reduce circuit chip area by approximately 50%every two years. The chip area reduction provides an economic benefitfor migrating to newer technologies. The 50% chip area reduction isachieved by reducing the feature sizes between 25% and 30%. Thereduction in feature size is enabled by improvements in manufacturingequipment and materials. For example, improvement in the lithographicprocess has enabled smaller feature sizes to be achieved, whileimprovement in chemical mechanical polishing (CMP) has in-part enabled ahigher number of interconnect layers.

In the evolution of lithography, as the minimum feature size approachedthe wavelength of the light source used to expose the feature shapes,unintended interactions occurred between neighboring features. Todayminimum feature sizes are approaching 45 nm (nanometers), while thewavelength of the light source used in the photolithography processremains at 193 nm. The difference between the minimum feature size andthe wavelength of light used in the photolithography process is definedas the lithographic gap. As the lithographic gap grows, the resolutioncapability of the lithographic process decreases.

An interference pattern occurs as each shape on the mask interacts withthe light. The interference patterns from neighboring shapes can createconstructive or destructive interference. In the case of constructiveinterference, unwanted shapes may be inadvertently created. In the caseof destructive interference, desired shapes may be inadvertentlyremoved. In either case, a particular shape is printed in a differentmanner than intended, possibly causing a device failure. Correctionmethodologies, such as optical proximity correction (OPC), attempt topredict the impact from neighboring shapes and modify the mask such thatthe printed shape is fabricated as desired. The quality of the lightinteraction prediction is declining as process geometries shrink and asthe light interactions become more complex.

In view of the foregoing, a solution is needed for managing lithographicgap issues as technology continues to progress toward smallersemiconductor device features sizes.

SUMMARY

In one embodiment, a semiconductor device is disclosed. Thesemiconductor device includes a substrate having a portion of thesubstrate formed to include a plurality of diffusion regions. Theplurality of diffusion regions respectively correspond to active areasof the portion of the substrate within which one or more processes areapplied to modify one or more electrical characteristics of the activeareas of the portion of the substrate. The plurality of diffusionregions include a first p-type diffusion region, a second p-typediffusion region, a first n-type diffusion region, and a second n-typediffusion region. The first p-type diffusion region includes a firstp-type active area electrically connected to a common node. The secondp-type diffusion region includes a second p-type active areaelectrically connected to the common node. The first n-type diffusionregion includes a first n-type active area electrically connected to thecommon node. The second n-type diffusion region includes a second n-typeactive area electrically connected to the common node.

The semiconductor device also includes a gate electrode level regionformed above the portion of the substrate. The gate electrode levelregion includes a number of conductive features defined to extend overthe substrate in only a first parallel direction. Each of the number ofconductive features within the gate electrode level region is fabricatedfrom a respective originating rectangular-shaped layout feature, suchthat a centerline of each respective originating rectangular-shapedlayout feature is aligned with a corresponding gate electrode trackextending across the substrate the first parallel direction. The numberof conductive features include conductive features that respectivelyform a first PMOS transistor device gate electrode, a second PMOStransistor device gate electrode, a first NMOS transistor device gateelectrode, and a second NMOS transistor device gate electrode.

The first PMOS transistor device gate electrode is formed to extendalong a first gate electrode track over the first p-type diffusionregion to electrically interface with the first p-type active area andthereby form a first PMOS transistor device. The second PMOS transistordevice gate electrode is formed to extend along a second gate electrodetrack over the second p-type diffusion region to electrically interfacewith the second p-type active area and thereby form a second PMOStransistor device. The first NMOS transistor device gate electrode isformed to extend along the first gate electrode track over the firstn-type diffusion region to electrically interface with the first n-typeactive area and thereby form a first NMOS transistor device. The secondNMOS transistor device gate electrode is formed to extend along thesecond gate electrode track over the second n-type diffusion region toelectrically interface with the second n-type active area and therebyform a second NMOS transistor device.

The first PMOS transistor device gate electrode is electricallyconnected to the second NMOS transistor device gate electrode through afirst set of interconnected conductors. The second PMOS transistordevice gate electrode is electrically connected to the first NMOStransistor device gate electrode through a second set of interconnectedconductors. The first and second sets of interconnected conductorstraverse across each other within different levels of the semiconductorchip. The first PMOS transistor device, the second PMOS transistordevice, the first NMOS transistor device, and the second NMOS transistordevice define a cross-coupled transistor configuration having commonlyoriented gate electrodes formed from respective rectangular-shapedlayout features.

Other aspects and advantages of the invention will become more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an SRAM bit cell circuit, in accordance with the priorart;

FIG. 1B shows the SRAM bit cell of FIG. 1A with the inverters expandedto reveal their respective internal transistor configurations, inaccordance with the prior art;

FIG. 2 shows a cross-coupled transistor configuration, in accordancewith one embodiment of the present invention;

FIG. 3A shows an example of gate electrode tracks defined within therestricted gate level layout architecture, in accordance with oneembodiment of the present invention;

FIG. 3B shows the exemplary restricted gate level layout architecture ofFIG. 3A with a number of exemplary gate level features defined therein,in accordance with one embodiment of the present invention;

FIG. 4 shows diffusion and gate level layouts of a cross-coupledtransistor configuration, in accordance with one embodiment of thepresent invention;

FIG. 5 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon three gate electrode tracks with crossing gate electrode connections;

FIG. 6 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon four gate electrode tracks with crossing gate electrode connections;

FIG. 7 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon two gate electrode tracks without crossing gate electrodeconnections;

FIG. 8 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon three gate electrode tracks without crossing gate electrodeconnections;

FIG. 9 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon four gate electrode tracks without crossing gate electrodeconnections;

FIG. 10 shows a multi-level layout including a cross-coupled transistorconfiguration defined on three gate electrode tracks with crossing gateelectrode connections, in accordance with one embodiment of the presentinvention;

FIG. 11 shows a multi-level layout including a cross-coupled transistorconfiguration defined on four gate electrode tracks with crossing gateelectrode connections, in accordance with one embodiment of the presentinvention;

FIG. 12 shows a multi-level layout including a cross-coupled transistorconfiguration defined on two gate electrode tracks without crossing gateelectrode connections, in accordance with one embodiment of the presentinvention;

FIG. 13 shows a multi-level layout including a cross-coupled transistorconfiguration defined on three gate electrode tracks without crossinggate electrode connections, in accordance with one embodiment of thepresent invention;

FIG. 14A shows a generalized multiplexer circuit in which all fourcross-coupled transistors are directly connected to the common node, inaccordance with one embodiment of the present invention;

FIG. 14B shows an exemplary implementation of the multiplexer circuit ofFIG. 14A with a detailed view of the pull up logic, and the pull downlogic, in accordance with one embodiment of the present invention;

FIG. 14C shows a multi-level layout of the multiplexer circuit of FIG.14B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 15A shows the multiplexer circuit of FIG. 14A in which twocross-coupled transistors remain directly connected to the common node,and in which two cross-coupled transistors are positioned outside thepull up logic and pull down logic, respectively, relative to the commonnode, in accordance with one embodiment of the present invention;

FIG. 15B shows an exemplary implementation of the multiplexer circuit ofFIG. 15A with a detailed view of the pull up logic and the pull downlogic, in accordance with one embodiment of the present invention;

FIG. 15C shows a multi-level layout of the multiplexer circuit of FIG.15B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 16A shows a generalized multiplexer circuit in which thecross-coupled transistors are connected to form two transmission gatesto the common node, in accordance with one embodiment of the presentinvention;

FIG. 16B shows an exemplary implementation of the multiplexer circuit ofFIG. 16A with a detailed view of the driving logic, in accordance withone embodiment of the present invention;

FIG. 16C shows a multi-level layout of the multiplexer circuit of FIG.16B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 17A shows a generalized multiplexer circuit in which twotransistors of the four cross-coupled transistors are connected to forma transmission gate to the common node, in accordance with oneembodiment of the present invention;

FIG. 17B shows an exemplary implementation of the multiplexer circuit ofFIG. 17A with a detailed view of the driving logic, in accordance withone embodiment of the present invention;

FIG. 17C shows a multi-level layout of the multiplexer circuit of FIG.17B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 18A shows a generalized latch circuit implemented using thecross-coupled transistor configuration, in accordance with oneembodiment of the present invention;

FIG. 18B shows an exemplary implementation of the latch circuit of FIG.18A with a detailed view of the pull up driver logic, the pull downdriver logic, the pull up feedback logic, and the pull down feedbacklogic, in accordance with one embodiment of the present invention;

FIG. 18C shows a multi-level layout of the latch circuit of FIG. 18Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 19A shows the latch circuit of FIG. 18A in which two cross-coupledtransistors remain directly connected to the common node, and in whichtwo cross-coupled transistors are positioned outside the pull up driverlogic and pull down driver logic, respectively, relative to the commonnode, in accordance with one embodiment of the present invention;

FIG. 19B shows an exemplary implementation of the latch circuit of FIG.19A with a detailed view of the pull up driver logic, the pull downdriver logic, the pull up feedback logic, and the pull down feedbacklogic, in accordance with one embodiment of the present invention;

FIG. 19C shows a multi-level layout of the latch circuit of FIG. 19Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 20A shows the latch circuit of FIG. 18A in which two cross-coupledtransistors remain directly connected to the common node, and in whichtwo cross-coupled transistors are positioned outside the pull upfeedback logic and pull down feedback logic, respectively, relative tothe common node, in accordance with one embodiment of the presentinvention;

FIG. 20B shows an exemplary implementation of the latch circuit of FIG.20A with a detailed view of the pull up driver logic, the pull downdriver logic, the pull up feedback logic, and the pull down feedbacklogic, in accordance with one embodiment of the present invention;

FIG. 20C shows a multi-level layout of the latch circuit of FIG. 20Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 21A shows a generalized latch circuit in which cross-coupledtransistors are connected to form two transmission gates to the commonnode, in accordance with one embodiment of the present invention;

FIG. 21B shows an exemplary implementation of the latch circuit of FIG.21A with a detailed view of the driving logic and the feedback logic, inaccordance with one embodiment of the present invention;

FIG. 21C shows a multi-level layout of the latch circuit of FIG. 21Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 22A shows a generalized latch circuit in which two transistors ofthe four cross-coupled transistors are connected to form a transmissiongate to the common node, in accordance with one embodiment of thepresent invention;

FIG. 22B shows an exemplary implementation of the latch circuit of FIG.22A with a detailed view of the driving logic, the pull up feedbacklogic, and the pull down feedback logic, in accordance with oneembodiment of the present invention;

FIG. 22C shows a multi-level layout of the latch circuit of FIG. 22Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention;

FIG. 23 shows an embodiment in which two PMOS transistors of thecross-coupled transistors are respectively disposed over physicallyseparated p-type diffusion regions, two NMOS transistors of thecross-coupled transistors are disposed over a common n-type diffusionregion, and the p-type and n-type diffusion regions associated with thecross-coupled transistors are electrically connected to a common node;

FIG. 24 shows an embodiment in which two PMOS transistors of thecross-coupled transistors are disposed over a common p-type diffusionregion, two NMOS transistors of the cross-coupled transistors arerespectively disposed over physically separated n-type diffusionregions, and the p-type and n-type diffusion regions associated with thecross-coupled transistors are electrically connected to a common node;and

FIG. 25 shows an embodiment in which two PMOS transistors of thecross-coupled transistors are respectively disposed over physicallyseparated p-type diffusion regions, two NMOS transistors of thecross-coupled transistors are respectively disposed over physicallyseparated n-type diffusion regions, and the p-type and n-type diffusionregions associated with the cross-coupled transistors are electricallyconnected to a common node;

FIGS. 26-99, 150-157, and 168-172 illustrate various cross-coupledtransistor layout embodiments in which two PMOS transistors of thecross-coupled transistors are disposed over a common p-type diffusionregion, two NMOS transistors of the cross-coupled transistors aredisposed over a common n-type diffusion region, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node;

FIGS. 103, 105, 112-149, 167, 184, and 186 illustrate variouscross-coupled transistor layout embodiments in which two PMOStransistors of the cross-coupled transistors are respectively disposedover physically separated p-type diffusion regions, two NMOS transistorsof the cross-coupled transistors are disposed over a common n-typediffusion region, and the p-type and n-type diffusion regions associatedwith the cross-coupled transistors are electrically connected to acommon node;

FIGS. 158-166, 173-183, 185, and 187-191 illustrate variouscross-coupled transistor layout embodiments in which two PMOStransistors of the cross-coupled transistors are respectively disposedover physically separated p-type diffusion regions, two NMOS transistorsof the cross-coupled transistors are respectively disposed overphysically separated n-type diffusion regions, and the p-type and n-typediffusion regions associated with the cross-coupled transistors areelectrically connected to a common node;

FIGS. 100, 101, 102, 104, and 106-111 show exemplary cross-coupledtransistor layouts in which the n-type and p-type diffusion regions ofthe cross-coupled transistors are shown to be electrically connected toa common node;

FIG. 192 shows another exemplary cross-couple transistor layout in whichthe common diffusion node shared between the cross-coupled transistors16601 p, 16603 p, 16605 p, and 16607 p has one or more transistorsdefined thereover.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

SRAM Bit Cell Configuration

FIG. 1A shows an SRAM (Static Random Access Memory) bit cell circuit, inaccordance with the prior art. The SRAM bit cell includes twocross-coupled inverters 106 and 102. Specifically, an output 106B ofinverter 106 is connected to an input 102A of inverter 102, and anoutput 102B of inverter 102 is connected to an input 106A of inverter106. The SRAM bit cell further includes two NMOS pass transistors 100and 104. The NMOS pass transistor 100 is connected between a bit-line103 and a node 109 corresponding to both the output 106B of inverter 106and the input 102A of inverter 102. The NMOS pass transistor 104 isconnected between a bit-line 105 and a node 111 corresponding to boththe output 102B of inverter 102 and the input 106A of inverter 106.Also, the respective gates of NMOS pass transistors 100 and 104 are eachconnected to a word line 107, which controls access to the SRAM bit cellthrough the NMOS pass transistors 100 and 104. The SRAM bit cellrequires bi-directional write, which means that when bit-line 103 isdriven high, bit-line 105 is driven low, vice-versa. It should beunderstood by those skilled in the art that a logic state stored in theSRAM bit cell is maintained in a complementary manner by nodes 109 and111.

FIG. 1B shows the SRAM bit cell of FIG. 1A with the inverters 106 and102 expanded to reveal their respective internal transistorconfigurations, in accordance with the prior art. The inverter 106include a PMOS transistor 115 and an NMOS transistor 113. The respectivegates of the PMOS and NMOS transistors 115, 113 are connected togetherto form the input 106A of inverter 106. Also, each of PMOS and NMOStransistors 115, 113 have one of their respective terminals connectedtogether to form the output 106B of inverter 106. A remaining terminalof PMOS transistor 115 is connected to a power supply 117. A remainingterminal of NMOS transistor 113 is connected to a ground potential 119.Therefore, PMOS and NMOS transistors 115, 113 are activated in acomplementary manner. When a high logic state is present at the input106A of the inverter 106, the NMOS transistor 113 is turned on and thePMOS transistor 115 is turned off, thereby causing a low logic state tobe generated at output 106B of the inverter 106. When a low logic stateis present at the input 106A of the inverter 106, the NMOS transistor113 is turned off and the PMOS transistor 115 is turned on, therebycausing a high logic state to be generated at output 106B of theinverter 106.

The inverter 102 is defined in an identical manner to inverter 106. Theinverter 102 include a PMOS transistor 121 and an NMOS transistor 123.The respective gates of the PMOS and NMOS transistors 121, 123 areconnected together to form the input 102A of inverter 102. Also, each ofPMOS and NMOS transistors 121, 123 have one of their respectiveterminals connected together to form the output 102B of inverter 102. Aremaining terminal of PMOS transistor 121 is connected to the powersupply 117. A remaining terminal of NMOS transistor 123 is connected tothe ground potential 119. Therefore, PMOS and NMOS transistors 121, 123are activated in a complementary manner. When a high logic state ispresent at the input 102A of the inverter 102, the NMOS transistor 123is turned on and the PMOS transistor 121 is turned off, thereby causinga low logic state to be generated at output 102B of the inverter 102.When a low logic state is present at the input 102A of the inverter 102,the NMOS transistor 123 is turned off and the PMOS transistor 121 isturned on, thereby causing a high logic state to be generated at output102B of the inverter 102.

Cross-Coupled Transistor Configuration

FIG. 2 shows a cross-coupled transistor configuration, in accordancewith one embodiment of the present invention. The cross-coupledtransistor configuration includes four transistors: a PMOS transistor401, an NMOS transistor 405, a PMOS transistor 403, and an NMOStransistor 407. The PMOS transistor 401 has one terminal connected topull up logic 209A, and its other terminal connected to a common node495. The NMOS transistor 405 has one terminal connected to pull downlogic 211A, and its other terminal connected to the common node 495. ThePMOS transistor 403 has one terminal connected to pull up logic 209B,and its other terminal connected to the common node 495. The NMOStransistor 407 has one terminal connected to pull down logic 211B, andits other terminal connected to the common node 495. Respective gates ofthe PMOS transistor 401 and the NMOS transistor 407 are both connectedto a gate node 491. Respective gates of the NMOS transistor 405 and thePMOS transistor 403 are both connected to a gate node 493. The gatenodes 491 and 493 are also referred to as control nodes 491 and 493,respectively. Moreover, each of the common node 495, the gate node 491,and the gate node 493 can be referred to as an electrical connection495, 491, 493, respectively.

Based on the foregoing, the cross-coupled transistor configurationincludes four transistors: 1) a first PMOS transistor, 2) a first NMOStransistor, 3) a second PMOS transistor, and 4) a second NMOStransistor. Furthermore, the cross-coupled transistor configurationincludes three required electrical connections: 1) each of the fourtransistors has one of its terminals connected to a same common node, 2)gates of one PMOS transistor and one NMOS transistor are both connectedto a first gate node, and 3) gates of the other PMOS transistor and theother NMOS transistor are both connected to a second gate node.

It should be understood that the cross-coupled transistor configurationof FIG. 2 represents a basic configuration of cross-coupled transistors.In other embodiments, additional circuitry components can be connectedto any node within the cross-coupled transistor configuration of FIG. 2.Moreover, in other embodiments, additional circuitry components can beinserted between any one or more of the cross-coupled transistors (401,405, 403, 407) and the common node 495, without departing from thecross-coupled transistor configuration of FIG. 2.

Difference Between SRAM Bit Cell and Cross-Coupled TransistorConfigurations

It should be understood that the SRAM bit cell of FIGS. 1A-1B does notinclude a cross-coupled transistor configuration. In particular, itshould be understood that the cross-coupled “inverters” 106 and 102within the SRAM bit cell neither represent nor infer a cross-coupled“transistor” configuration. As discussed above, the cross-coupledtransistor configuration requires that each of the four transistors hasone of its terminals electrically connected to the same common node.This does not occur in the SRAM bit cell.

With reference to the SRAM bit cell in FIG. 1B, the terminals of PMOStransistor 115 and NMOS transistor 113 are connected together at node109, but the terminals of PMOS transistor 121 and NMOS transistor 123are connected together at node 111. More specifically, the terminals ofPMOS transistor 115 and NMOS transistor 113 that are connected togetherat the output 106B of the inverter are connected to the gates of each ofPMOS transistor 121 and NMOS transistor 123, and therefore are notconnected to both of the terminals of PMOS transistor 121 and NMOStransistor 123. Therefore, the SRAM bit cell does not include fourtransistors (two PMOS and two NMOS) that each have one of its terminalsconnected together at a same common node. Consequently, the SRAM bitcell does represent or include across-coupled transistor configuration,such as described with regard to FIG. 2.

Restricted Gate Level Layout Architecture

The present invention implements a restricted gate level layoutarchitecture within a portion of a semiconductor chip. For the gatelevel, a number of parallel virtual lines are defined to extend acrossthe layout. These parallel virtual lines are referred to as gateelectrode tracks, as they are used to index placement of gate electrodesof various transistors within the layout. In one embodiment, theparallel virtual lines which form the gate electrode tracks are definedby a perpendicular spacing therebetween equal to a specified gateelectrode pitch. Therefore, placement of gate electrode segments on thegate electrode tracks corresponds to the specified gate electrode pitch.In another embodiment the gate electrode tracks are spaced at variablepitches greater than or equal to a specified gate electrode pitch.

FIG. 3A shows an example of gate electrode tracks 301A-301E definedwithin the restricted gate level layout architecture, in accordance withone embodiment of the present invention. Gate electrode tracks 301A-301Eare formed by parallel virtual lines that extend across the gate levellayout of the chip, with a perpendicular spacing therebetween equal to aspecified gate electrode pitch 307. For illustrative purposes,complementary diffusion regions 303 and 305 are shown in FIG. 3A. Itshould be understood that the diffusion regions 303 and 305 are definedin the diffusion level below the gate level. Also, it should beunderstood that the diffusion regions 303 and 305 are provided by way ofexample and in no way represent any limitation on diffusion region size,shape, and/or placement within the diffusion level relative to therestricted gate level layout architecture.

Within the restricted gate level layout architecture, a gate levelfeature layout channel is defined about a given gate electrode track soas to extend between gate electrode tracks adjacent to the given gateelectrode track. For example, gate level feature layout channels 301A-1through 301E-1 are defined about gate electrode tracks 301A through301E, respectively. It should be understood that each gate electrodetrack has a corresponding gate level feature layout channel. Also, forgate electrode tracks positioned adjacent to an edge of a prescribedlayout space, e.g., adjacent to a cell boundary, the corresponding gatelevel feature layout channel extends as if there were a virtual gateelectrode track outside the prescribed layout space, as illustrated bygate level feature layout channels 301A-1 and 301E-1. It should befurther understood that each gate level feature layout channel isdefined to extend along an entire length of its corresponding gateelectrode track. Thus, each gate level feature layout channel is definedto extend across the gate level layout within the portion of the chip towhich the gate level layout is associated.

Within the restricted gate level layout architecture, gate levelfeatures associated with a given gate electrode track are defined withinthe gate level feature layout channel associated with the given gateelectrode track. A contiguous gate level feature can include both aportion which defines a gate electrode of a transistor, and a portionthat does not define a gate electrode of a transistor. Thus, acontiguous gate level feature can extend over both a diffusion regionand a dielectric region of an underlying chip level. In one embodiment,each portion of a gate level feature that forms a gate electrode of atransistor is positioned to be substantially centered upon a given gateelectrode track. Furthermore, in this embodiment, portions of the gatelevel feature that do not form a gate electrode of a transistor can bepositioned within the gate level feature layout channel associated withthe given gate electrode track. Therefore, a given gate level featurecan be defined essentially anywhere within a given gate level featurelayout channel, so long as gate electrode portions of the given gatelevel feature are centered upon the gate electrode track correspondingto the given gate level feature layout channel, and so long as the givengate level feature complies with design rule spacing requirementsrelative to other gate level features in adjacent gate level layoutchannels. Additionally, physical contact is prohibited between gatelevel features defined in gate level feature layout channels that areassociated with adjacent gate electrode tracks.

FIG. 3B shows the exemplary restricted gate level layout architecture ofFIG. 3A with a number of exemplary gate level features 309-323 definedtherein, in accordance with one embodiment of the present invention. Thegate level feature 309 is defined within the gate level feature layoutchannel 301A-1 associated with gate electrode track 301A. The gateelectrode portions of gate level feature 309 are substantially centeredupon the gate electrode track 301A. Also, the non-gate electrodeportions of gate level feature 309 maintain design rule spacingrequirements with gate level features 311 and 313 defined withinadjacent gate level feature layout channel 301B-1. Similarly, gate levelfeatures 311-323 are defined within their respective gate level featurelayout channel, and have their gate electrode portions substantiallycentered upon the gate electrode track corresponding to their respectivegate level feature layout channel. Also, it should be appreciated thateach of gate level features 311-323 maintains design rule spacingrequirements with gate level features defined within adjacent gate levelfeature layout channels, and avoids physical contact with any anothergate level feature defined within adjacent gate level feature layoutchannels.

A gate electrode corresponds to a portion of a respective gate levelfeature that extends over a diffusion region, wherein the respectivegate level feature is defined in its entirety within a gate levelfeature layout channel. Each gate level feature is defined within itsgate level feature layout channel without physically contacting anothergate level feature defined within an adjoining gate level feature layoutchannel. As illustrated by the example gate level feature layoutchannels 301A-1 through 301E-1 of FIG. 3B, each gate level featurelayout channel is associated with a given gate electrode track andcorresponds to a layout region that extends along the given gateelectrode track and perpendicularly outward in each opposing directionfrom the given gate electrode track to a closest of either an adjacentgate electrode track or a virtual gate electrode track outside a layoutboundary.

Some gate level features may have one or more contact head portionsdefined at any number of locations along their length. A contact headportion of a given gate level feature is defined as a segment of thegate level feature having a height and a width of sufficient size toreceive a gate contact structure, wherein “width” is defined across thesubstrate in a direction perpendicular to the gate electrode track ofthe given gate level feature, and wherein “height” is defined across thesubstrate in a direction parallel to the gate electrode track of thegiven gate level feature. It should be appreciated that a contact headof a gate level feature, when viewed from above, can be defined byessentially any layout shape, including a square or a rectangle. Also,depending on layout requirements and circuit design, a given contacthead portion of a gate level feature may or may not have a gate contactdefined thereabove.

A gate level of the various embodiments disclosed herein is defined as arestricted gate level, as discussed above. Some of the gate levelfeatures form gate electrodes of transistor devices. Others of the gatelevel features can form conductive segments extending between two pointswithin the gate level. Also, others of the gate level features may benon-functional with respect to integrated circuit operation. It shouldbe understood that the each of the gate level features, regardless offunction, is defined to extend across the gate level within theirrespective gate level feature layout channels without physicallycontacting other gate level features defined with adjacent gate levelfeature layout channels.

In one embodiment, the gate level features are defined to provide afinite number of controlled layout shape-to-shape lithographicinteractions which can be accurately predicted and optimized for inmanufacturing and design processes. In this embodiment, the gate levelfeatures are defined to avoid layout shape-to-shape spatialrelationships which would introduce adverse lithographic interactionwithin the layout that cannot be accurately predicted and mitigated withhigh probability. However, it should be understood that changes indirection of gate level features within their gate level layout channelsare acceptable when corresponding lithographic interactions arepredictable and manageable.

It should be understood that each of the gate level features, regardlessof function, is defined such that no gate level feature along a givengate electrode track is configured to connect directly within the gatelevel to another gate level feature defined along a different gateelectrode track without utilizing a non-gate level feature. Moreover,each connection between gate level features that are placed withindifferent gate level layout channels associated with different gateelectrode tracks is made through one or more non-gate level features,which may be defined in higher interconnect levels, i.e., through one ormore interconnect levels above the gate level, or by way of localinterconnect features at or below the gate level.

Cross-Coupled Transistor Layouts

As discussed above, the cross-coupled transistor configuration includesfour transistors (2 PMOS transistors and 2 NMOS transistors). In variousembodiments of the present invention, gate electrodes defined inaccordance with the restricted gate level layout architecture arerespectively used to form the four transistors of a cross-coupledtransistor configuration layout. FIG. 4 shows diffusion and gate levellayouts of a cross-coupled transistor configuration, in accordance withone embodiment of the present invention. The cross-coupled transistorlayout of FIG. 4 includes the first PMOS transistor 401 defined by agate electrode 401A extending along a gate electrode track 450 and overa p-type diffusion region 480. The first NMOS transistor 407 is definedby a gate electrode 407A extending along a gate electrode track 456 andover an n-type diffusion region 486. The second PMOS transistor 403 isdefined by a gate electrode 403A extending along the gate electrodetrack 456 and over a p-type diffusion region 482. The second NMOStransistor 405 is defined by a gate electrode 405A extending along thegate electrode track 450 and over an n-type diffusion region 484.

The gate electrodes 401A and 407A of the first PMOS transistor 401 andfirst NMOS transistor 407, respectively, are electrically connected tothe first gate node 491 so as to be exposed to a substantiallyequivalent gate electrode voltage. Similarly, the gate electrodes 403Aand 405A of the second PMOS transistor 403 and second NMOS transistor405, respectively, are electrically connected to the second gate node493 so as to be exposed to a substantially equivalent gate electrodevoltage. Also, each of the four transistors 401, 403, 405, 407 has arespective diffusion terminal electrically connected to the commonoutput node 495.

The cross-coupled transistor layout can be implemented in a number ofdifferent ways within the restricted gate level layout architecture. Inthe exemplary embodiment of FIG. 4, the gate electrodes 401A and 405A ofthe first PMOS transistor 401 and second NMOS transistor 405 arepositioned along the same gate electrode track 450. Similarly, the gateelectrodes 403A and 407A of the second PMOS transistor 403 and secondNMOS transistor 407 are positioned along the same gate electrode track456. Thus, the particular embodiment of FIG. 4 can be characterized as across-coupled transistor configuration defined on two gate electrodetracks with crossing gate electrode connections.

FIG. 5 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon three gate electrode tracks with crossing gate electrode connections.Specifically, the gate electrode 401A of the first PMOS transistor 401is defined on the gate electrode track 450. The gate electrode 403A ofthe second PMOS transistor 403 is defined on the gate electrode track456. The gate electrode 407A of the first NMOS transistor 407 is definedon a gate electrode track 456. And, the gate electrode 405A of thesecond NMOS transistor 405 is defined on a gate electrode track 448.Thus, the particular embodiment of FIG. 5 can be characterized as across-coupled transistor configuration defined on three gate electrodetracks with crossing gate electrode connections.

FIG. 6 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon four gate electrode tracks with crossing gate electrode connections.Specifically, the gate electrode 401A of the first PMOS transistor 401is defined on the gate electrode track 450. The gate electrode 403A ofthe second PMOS transistor 403 is defined on the gate electrode track456. The gate electrode 407A of the first NMOS transistor 407 is definedon a gate electrode track 458. And, the gate electrode 405A of thesecond NMOS transistor 405 is defined on a gate electrode track 454.Thus, the particular embodiment of FIG. 6 can be characterized as across-coupled transistor configuration defined on four gate electrodetracks with crossing gate electrode connections.

FIG. 7 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon two gate electrode tracks without crossing gate electrodeconnections. Specifically, the gate electrode 401A of the first PMOStransistor 401 is defined on the gate electrode track 450. The gateelectrode 407A of the first NMOS transistor 407 is also defined on agate electrode track 450. The gate electrode 403A of the second PMOStransistor 403 is defined on the gate electrode track 456. And, the gateelectrode 405A of the second NMOS transistor 405 is also defined on agate electrode track 456. Thus, the particular embodiment of FIG. 7 canbe characterized as a cross-coupled transistor configuration defined ontwo gate electrode tracks without crossing gate electrode connections.

FIG. 8 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon three gate electrode tracks without crossing gate electrodeconnections. Specifically, the gate electrode 401A of the first PMOStransistor 401 is defined on the gate electrode track 450. The gateelectrode 407A of the first NMOS transistor 407 is also defined on agate electrode track 450. The gate electrode 403A of the second PMOStransistor 403 is defined on the gate electrode track 454. And, the gateelectrode 405A of the second NMOS transistor 405 is defined on a gateelectrode track 456. Thus, the particular embodiment of FIG. 8 can becharacterized as a cross-coupled transistor configuration defined onthree gate electrode tracks without crossing gate electrode connections.

FIG. 9 shows a variation of the cross-coupled transistor configurationof FIG. 4 in which the cross-coupled transistor configuration is definedon four gate electrode tracks without crossing gate electrodeconnections. Specifically, the gate electrode 401A of the first PMOStransistor 401 is defined on the gate electrode track 450. The gateelectrode 403A of the second PMOS transistor 403 is defined on the gateelectrode track 454. The gate electrode 407A of the first NMOStransistor 407 is defined on a gate electrode track 452. And, the gateelectrode 405A of the second NMOS transistor 405 is defined on a gateelectrode track 456. Thus, the particular embodiment of FIG. 9 can becharacterized as a cross-coupled transistor configuration defined onfour gate electrode tracks without crossing gate electrode connections.

It should be appreciated that although the cross-coupled transistors401, 403, 405, 407 of FIGS. 4-9 are depicted as having their ownrespective diffusion region 480, 482, 484, 486, respectively, otherembodiments may utilize a contiguous p-type diffusion region for PMOStransistors 401 and 403, and/or utilize a contiguous n-type diffusionregion for NMOS transistors 405 and 407. Moreover, although the examplelayouts of FIGS. 4-9 depict the p-type diffusion regions 480 and 482 ina vertically aligned position, it should be understood that the p-typediffusion regions 480 and 482 may not be vertically aligned in otherembodiments. Similarly, although the example layouts of FIGS. 4-9 depictthe n-type diffusion regions 484 and 486 in a vertically alignedposition, it should be understood that the n-type diffusion regions 484and 486 may not be vertically aligned in other embodiments.

For example, the cross-coupled transistor layout of FIG. 4 includes thefirst PMOS transistor 401 defined by the gate electrode 401A extendingalong the gate electrode track 450 and over a first p-type diffusionregion 480. And, the second PMOS transistor 403 is defined by the gateelectrode 403A extending along the gate electrode track 456 and over asecond p-type diffusion region 482. The first NMOS transistor 407 isdefined by the gate electrode 407A extending along the gate electrodetrack 456 and over a first n-type diffusion region 486. And, the secondNMOS transistor 405 is defined by the gate electrode 405A extendingalong the gate electrode track 450 and over a second n-type diffusionregion 484.

The gate electrode tracks 450 and 456 extend in a first paralleldirection. At least a portion of the first p-type diffusion region 480and at least a portion of the second p-type diffusion region 482 areformed over a first common line of extent that extends across thesubstrate perpendicular to the first parallel direction of the gateelectrode tracks 450 and 456. Additionally, at least a portion of thefirst u-type diffusion region 486 and at least a portion of the secondn-type diffusion region 484 are formed over a second common line ofextent that extends across the substrate perpendicular to the firstparallel direction of the gate electrode tracks 450 and 456.

FIG. 14C shows that two PMOS transistors (401A and 403A) of thecross-coupled transistors are disposed over a common p-type diffusionregion (PDIFF), two NMOS transistors (405A and 407A) of thecross-coupled transistors are disposed over a common n-type diffusionregion (NDIFF), and the p-type (PDIFF) and n-type (NDIFF) diffusionregions associated with the cross-coupled transistors are electricallyconnected to a common node 495. The gate electrodes of the cross-coupledtransistors (401A, 403A, 405A, 407A) extend in a first paralleldirection. At least a portion of a first p-type diffusion regionassociated with the first PMOS transistor 401A and at least a portion ofa second p-type diffusion region associated with the second PMOStransistor 403A are formed over a first common line of extent thatextends across the substrate perpendicular to the first paralleldirection of the gate electrodes. Additionally, at least a portion of afirst n-type diffusion region associated with the first NMOS transistor405A and at least a portion of a second n-type diffusion regionassociated with the second NMOS transistor 407A are formed over a secondcommon line of extent that extends across the substrate perpendicular tothe first parallel direction of the gate electrodes.

In another embodiment, two PMOS transistors of the cross-coupledtransistors are respectively disposed over physically separated p-typediffusion regions, two NMOS transistors of the cross-coupled transistorsare disposed over a common n-type diffusion region, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node. FIG. 23 illustrates across-coupled transistor layout embodiment in which two PMOS transistors(2301 and 2303) of the cross-coupled transistors are respectivelydisposed over physically separated p-type diffusion regions (2302 and2304), two NMOS transistors (2305 and 2307) of the cross-coupledtransistors are disposed over a common n-type diffusion region 2306, andthe p-type (2302, 2304) and n-type 2306 diffusion regions associatedwith the cross-coupled transistors are electrically connected to acommon node 2309.

FIG. 23 shows that the gate electrodes of the cross-coupled transistors(2301, 2303, 2305, 2307) extend in a first parallel direction 2311. FIG.23 also shows that the first 2302 and second 2304 p-type diffusionregions are formed in a spaced apart manner relative to the firstparallel direction 2311 of the gate electrodes, such that no single lineof extent that extends across the substrate in a direction 2313perpendicular to the first parallel direction 2311 of the gateelectrodes intersects both the first 2302 and second 2304 p-typediffusion regions. Also, FIG. 23 shows that at least a portion of afirst n-type diffusion region (part of 2306) associated with a firstNMOS transistor 2305 and at least a portion of a second n-type diffusionregion (part of 2306) associated with a second NMOS transistor 2307 areformed over a common line of extent that extends across the substrate inthe direction 2313 perpendicular to the first parallel direction 2311 ofthe gate electrodes.

In another embodiment, two PMOS transistors of the cross-coupledtransistors are disposed over a common p-type diffusion region, two NMOStransistors of the cross-coupled transistors are respectively disposedover physically separated n-type diffusion regions, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node. FIG. 24 shows thecross-coupled transistor embodiment of FIG. 23, with the p-type (2302and 2304) and n-type 2306 diffusion regions of FIG. 23 reversed ton-type (2402 and 2404) and p-type 2406 diffusion regions, respectively.FIG. 24 illustrates a cross-coupled transistor layout embodiment inwhich two PMOS transistors (2405 and 2407) of the cross-coupledtransistors are disposed over a common p-type diffusion region 2406, twoNMOS transistors (2401 and 2403) of the cross-coupled transistors arerespectively disposed over physically separated n-type diffusion regions(2402 and 2404), and the p-type 2406 and n-type (2402 and 2404)diffusion regions associated with the cross-coupled transistors areelectrically connected to a common node 2409.

FIG. 24 shows that the gate electrodes of the cross-coupled transistors(2401, 2403, 2405, 2407) extend in a first parallel direction 2411. FIG.24 also shows that at least a portion of a first p-type diffusion region(part of 2406) associated with a first PMOS transistor 2405 and at leasta portion of a second p-type diffusion region (part of 2406) associatedwith a second PMOS transistor 2407 are formed over a common line ofextent that extends across the substrate in a direction 2413perpendicular to the first parallel direction 2411 of the gateelectrodes. Also, FIG. 24 shows that the first 2402 and second 2404n-type diffusion regions are formed in a spaced apart manner relative tothe first parallel direction 2411, such that no single line of extentthat extends across the substrate in the direction 2413 perpendicular tothe first parallel direction 2411 of the gate electrodes intersects boththe first 2402 and second 2404 n-type diffusion regions.

In yet another embodiment, two PMOS transistors of the cross-coupledtransistors are respectively disposed over physically separated p-typediffusion regions, two NMOS transistors of the cross-coupled transistorsare respectively disposed over physically separated n-type diffusionregions, and the p-type and n-type diffusion regions associated with thecross-coupled transistors are electrically connected to a common node.FIG. 25 shows a cross-coupled transistor layout embodiment in which twoPMOS transistors (2501 and 2503) of the cross-coupled transistors arerespectively disposed over physically separated p-type diffusion regions(2502 and 2504), two NMOS transistors (2505 and 2507) of thecross-coupled transistors are respectively disposed over physicallyseparated n-type diffusion regions (2506 and 2508), and the p-type (2502and 2504) and n-type (2506 and 2508) diffusion regions associated withthe cross-coupled transistors are electrically connected to a commonnode 2509.

FIG. 25 shows that the gate electrodes of the cross-coupled transistors(2501, 2503, 2505, 2507) extend in a first parallel direction 2511. FIG.25 also shows that the first 2502 and second 2504 p-type diffusionregions are formed in a spaced apart manner relative to the firstparallel direction 2511, such that no single line of extent that extendsacross the substrate in a direction 2513 perpendicular to the firstparallel direction 2511 of the gate electrodes intersects both the first2502 and second 2504 p-type diffusion regions. Also, FIG. 25 shows thatthe first 2506 and second 2508 n-type diffusion regions are formed in aspaced apart manner relative to the first parallel direction 2511, suchthat no single line of extent that extends across the substrate in thedirection 2513 perpendicular to the first parallel direction 2511 of thegate electrodes intersects both the first 2506 and second 2508 n-typediffusion regions.

In FIGS. 4-9, the gate electrode connections are electricallyrepresented by lines 491 and 493, and the common node electricalconnection is represented by line 495. It should be understood that inlayout space each of the gate electrode electrical connections 491, 493,and the common node electrical connection 495 can be structurallydefined by a number of layout shapes extending through multiple chiplevels. FIGS. 10-13 show examples of how the gate electrode electricalconnections 491, 493, and the common node electrical connection 495 canbe defined in different embodiments. It should be understood that theexample layouts of FIGS. 10-13 are provided by way of example and in noway represent an exhaustive set of possible multi-level connections thatcan be utilized for the gate electrode electrical connections 491, 493,and the common node electrical connection 495.

FIG. 10 shows a multi-level layout including a cross-coupled transistorconfiguration defined on three gate electrode tracks with crossing gateelectrode connections, in accordance with one embodiment of the presentinvention. The layout of FIG. 10 represents an exemplary implementationof the cross-coupled transistor embodiment of FIG. 5. The electricalconnection 491 between the gate electrode 401A of the first PMOStransistor 401 and the gate electrode 407A of the first NMOS transistor407 is formed by a multi-level connection that includes a gate contact1001, a (two-dimensional) metal-1 structure 1003, and a gate contact1005. The electrical connection 493 between the gate electrode 403A ofthe second PMOS transistor 403 and the gate electrode 405A of the secondNMOS transistor 405 is formed by a multi-level connection that includesa gate contact 1007, a (two-dimensional) metal-1 structure 1009, and agate contact 1011. The output node electrical connection 495 is formedby a multi-level connection that includes a diffusion contact 1013, a(two-dimensional) metal-1 structure 1015, a diffusion contact 1017, anda diffusion contact 1019.

FIG. 11 shows a multi-level layout including a cross-coupled transistorconfiguration defined on four gate electrode tracks with crossing gateelectrode connections, in accordance with one embodiment of the presentinvention. The layout of FIG. 11 represents an exemplary implementationof the cross-coupled transistor embodiment of FIG. 6. The electricalconnection 491 between the gate electrode 401A of the first PMOStransistor 401 and the gate electrode 407A of the first NMOS transistor407 is formed by a multi-level connection that includes a gate contact1101, a (two-dimensional) metal-1 structure 1103, and a gate contact1105. The electrical connection 493 between the gate electrode 403A ofthe second PMOS transistor 403 and the gate electrode 405A of the secondNMOS transistor 405 is formed by a multi-level connection that includesa gate contact 1107, a (one-dimensional) metal-1 structure 1109, a via1111, a (one-dimensional) metal-2 structure 1113, a via 1115, a(one-dimensional) metal-1 structure 1117, and a gate contact 1119. Theoutput node electrical connection 495 is formed by a multi-levelconnection that includes a diffusion contact 1121, a (two-dimensional)metal-1 structure 1123, a diffusion contact 1125, and a diffusioncontact 1127.

FIG. 12 shows a multi-level layout including a cross-coupled transistorconfiguration defined on two gate electrode tracks without crossing gateelectrode connections, in accordance with one embodiment of the presentinvention. The layout of FIG. 12 represents an exemplary implementationof the cross-coupled transistor embodiment of FIG. 7. The gateelectrodes 401A and 407A of the first PMOS transistor 401 and first NMOStransistor 407, respectively, are formed by a contiguous gate levelstructure placed on the gate electrode track 450. Therefore, theelectrical connection 491 between the gate electrodes 401A and 407A ismade directly within the gate level along the single gate electrodetrack 450. Similarly, the gate electrodes 403A and 405A of the secondPMOS transistor 403 and second NMOS transistor 405, respectively, areformed by a contiguous gate level structure placed on the gate electrodetrack 456. Therefore, the electrical connection 493 between the gateelectrodes 403A and 405A is made directly within the gate level alongthe single gate electrode track 456. The output node electricalconnection 495 is formed by a multi-level connection that includes adiffusion contact 1205, a (one-dimensional) metal-1 structure 1207, anda diffusion contact 1209.

Further with regard to FIG. 12, it should be noted that when the gateelectrodes 401A and 407A of the first PMOS transistor 401 and first NMOStransistor 407, respectively, are formed by a contiguous gate levelstructure, and when the gate electrodes 403A and 405A of the second PMOStransistor 403 and second NMOS transistor 405, respectively, are formedby a contiguous gate level structure, the corresponding cross-coupledtransistor layout may include electrical connections between diffusionregions associated with the four cross-coupled transistors 401, 407,403, 405, that cross in layout space without electrical communicationtherebetween. For example, diffusion region 1220 of PMOS transistor 403is electrically connected to diffusion region 1222 of NMOS transistor407 as indicated by electrical connection 1224, and diffusion region1230 of PMOS transistor 401 is electrically connected to diffusionregion 1232 of NMOS transistor 405 as indicated by electrical connection1234, wherein electrical connections 1224 and 1234 cross in layout spacewithout electrical communication therebetween.

FIG. 13 shows a multi-level layout including a cross-coupled transistorconfiguration defined on three gate electrode tracks without crossinggate electrode connections, in accordance with one embodiment of thepresent invention. The layout of FIG. 13 represents an exemplaryimplementation of the cross-coupled transistor embodiment of FIG. 8. Thegate electrodes 401A and 407A of the first PMOS transistor 401 and firstNMOS transistor 407, respectively, are formed by a contiguous gate levelstructure placed on the gate electrode track 450. Therefore, theelectrical connection 491 between the gate electrodes 401A and 407A ismade directly within the gate level along the single gate electrodetrack 450. The electrical connection 493 between the gate electrode 403Aof the second PMOS transistor 403 and the gate electrode 405A of thesecond NMOS transistor 405 is formed by a multi-level connection thatincludes a gate contact 1303, a (one-dimensional) metal-1 structure1305, and a gate contact 1307. The output node electrical connection 495is formed by a multi-level connection that includes a diffusion contact1311, a (one-dimensional) metal-1 structure 1313, and a diffusioncontact 1315.

In one embodiment, electrical connection of the diffusion regions of thecross-coupled transistors to the common node 495 can be made using oneor more local interconnect conductors defined at or below the gate levelitself. This embodiment may also combine local interconnect conductorswith conductors in higher levels (above the gate level) by way ofcontacts and/or vias to make the electrical connection of the diffusionregions of the cross-coupled transistors to the common node 495.Additionally, in various embodiments, conductive paths used toelectrically connect the diffusion regions of the cross-coupledtransistors to the common node 495 can be defined to traverse overessentially any area of the chip as required to accommodate a routingsolution for the chip.

Also, it should be appreciated that because the n-type and p-typediffusion regions are physically separate, and because the p-typediffusion regions for the two PMOS transistors of the cross-coupledtransistors can be physically separate, and because the n-type diffusionregions for the two NMOS transistors of the cross-coupled transistorscan be physically separate, it is possible in various embodiments tohave each of the four cross-coupled transistors disposed at arbitrarylocations in the layout relative to each other. Therefore, unlessnecessitated by electrical performance or other layout influencingconditions, it is not required that the four cross-coupled transistorsbe located within a prescribed proximity to each other in the layout.Although, location of the cross-coupled transistors within a prescribedproximity to each other is not precluded, and may be desirable incertain circuit layouts.

In the exemplary embodiments disclosed herein, it should be understoodthat diffusion regions are not restricted in size. In other words, anygiven diffusion region can be sized in an arbitrary manner as requiredto satisfy electrical and/or layout requirements. Additionally, anygiven diffusion region can be shaped in an arbitrary manner as requiredto satisfy electrical and/or layout requirements. Also, it should beunderstood that the four transistors of the cross-coupled transistorconfiguration, as defined in accordance with the restricted gate levellayout architecture, are not required to be the same size. In differentembodiments, the four transistors of the cross-coupled transistorconfiguration can either vary in size (transistor width or transistorgate length) or have the same size, depending on the applicableelectrical and/or layout requirements.

Additionally, it should be understood that the four transistors of thecross-coupled transistor configuration are not required to be placed inclose proximity to each, although they may be closely placed in someembodiments. More specifically, because connections between thetransistors of the cross-coupled transistor configuration can be made byrouting through as least one higher interconnect level, there is freedomin placement of the four transistors of the cross-coupled transistorconfiguration relative to each other. Although, it should be understoodthat a proximity of the four transistors of the cross-coupled transistorconfiguration may be governed in certain embodiments by electricaland/or layout optimization requirements.

It should be appreciated that the cross-coupled transistorconfigurations and corresponding layouts implemented using therestricted gate level layout architecture, as described with regard toFIGS. 2-13, and/or variants thereof, can be used to form many differentelectrical circuits. For example, a portion of a modern semiconductorchip is likely to include a number of multiplexer circuits and/or latchcircuits. Such multiplexer and/or latch circuits can be defined usingcross-coupled transistor configurations and corresponding layouts basedon the restricted gate level layout architecture, as disclosed herein.Example multiplexer embodiments implemented using the restricted gatelevel layout architecture and corresponding cross-coupled transistorconfigurations are described with regard to FIGS. 14A-17C. Example latchembodiments implemented using the restricted gate level layoutarchitecture and corresponding cross-coupled transistor configurationsare described with regard to FIGS. 18A-22C. It should be understood thatthe multiplexer and latch embodiments described with regard to FIGS.14A-22C are provided by way of example and do not represent anexhaustive set of possible multiplexer and latch embodiments.

Example Multiplexer Embodiments

FIG. 14A shows a generalized multiplexer circuit in which all fourcross-coupled transistors 401, 405, 403, 407 are directly connected tothe common node 495, in accordance with one embodiment of the presentinvention. As previously discussed, gates of the first PMOS transistor401 and first NMOS transistor 407 are electrically connected, as shownby electrical connection 491. Also, gates of the second PMOS transistor403 and second NMOS transistor 405 are electrically connected, as shownby electrical connection 493. Pull up logic 1401 is electricallyconnected to the first PMOS transistor 401 at a terminal opposite thecommon node 495. Pull down logic 1403 is electrically connected to thesecond NMOS transistor 405 at a terminal opposite the common node 495.Also, pull up logic 1405 is electrically connected to the second PMOStransistor 403 at a terminal opposite the common node 495. Pull downlogic 1407 is electrically connected to the first NMOS transistor 407 ata terminal opposite the common node 495.

FIG. 14B shows an exemplary implementation of the multiplexer circuit ofFIG. 14A with a detailed view of the pull up logic 1401 and 1405, andthe pull down logic 1403 and 1407, in accordance with one embodiment ofthe present invention. The pull up logic 1401 is defined by a PMOStransistor 1401A connected between a power supply (VDD) and a terminal1411 of the first PMOS transistor 401 opposite the common node 495. Thepull down logic 1403 is defined by an NMOS transistor 1403A connectedbetween a ground potential (GND) and a terminal 1413 of the second NMOStransistor 405 opposite the common node 495. Respective gates of thePMOS transistor 1401A and NMOS transistor 1403A are connected togetherat a node 1415. The pull up logic 1405 is defined by a PMOS transistor1405A connected between the power supply (VDD) and a terminal 1417 ofthe second PMOS transistor 403 opposite the common node 495. The pulldown logic 1407 is defined by an NMOS transistor 1407A connected betweena ground potential (GND) and a terminal 1419 of the first NMOStransistor 407 opposite the common node 495. Respective gates of thePMOS transistor 1405A and NMOS transistor 1407A are connected togetherat a node 1421. It should be understood that the implementations of pullup logic 1401, 1405 and pull down logic 1403, 1407 as shown in FIG. 14Bare exemplary. In other embodiments, logic different than that shown inFIG. 14B can be used to implement the pull up logic 1401, 1405 and thepull down logic 1403, 1407.

FIG. 14C shows a multi-level layout of the multiplexer circuit of FIG.14B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1445, a (two-dimensional)metal-1 structure 1447, and a gate contact 1449. The electricalconnection 493 between the gate electrode 403A of the second PMOStransistor 403 and the gate electrode 405A of the second NMOS transistor405 is formed by a multi-level connection that includes a gate contact1431, a (one-dimensional) metal-1 structure 1433, a via 1435, a(one-dimensional) metal-2 structure 1436, a via 1437, a(one-dimensional) metal-1 structure 1439, and a gate contact 1441. Thecommon node electrical connection 495 is formed by a multi-levelconnection that includes a diffusion contact 1451, a (one-dimensional)metal-1 structure 1453, a via 1455, a (one-dimensional) metal-2structure 1457, a via 1459, a (one-dimensional) metal-1 structure 1461,and a diffusion contact 1463. Respective gates of the PMOS transistor1401A and NMOS transistor 1403A are connected to the node 1415 by a gatecontact 1443. Also, respective gates of the PMOS transistor 1405A andNMOS transistor 1407A are connected to the node 1421 by a gate contact1465.

FIG. 15A shows the multiplexer circuit of FIG. 14A in which the twocross-coupled transistors 401 and 405 remain directly connected to thecommon node 495, and in which the two cross-coupled transistors 403 and407 are positioned outside the pull up logic 1405 and pull down logic1407, respectively, relative to the common node 495, in accordance withone embodiment of the present invention. Pull up logic 1405 iselectrically connected between the second PMOS transistor 403 and thecommon node 495. Pull down logic 1407 is electrically connected betweenthe first NMOS transistor 407 and the common node 495. With theexception of repositioning the PMOS/NMOS transistors 403/407 outside oftheir pull up/down logic 1405/1407 relative to the common node 495, thecircuit of FIG. 15A is the same as the circuit of FIG. 14A.

FIG. 15B shows an exemplary implementation of the multiplexer circuit ofFIG. 15A with a detailed view of the pull up logic 1401 and 1405, andthe pull down logic 1403 and 1407, in accordance with one embodiment ofthe present invention. As previously discussed with regard to FIG. 14B,the pull up logic 1401 is defined by the PMOS transistor 1401A connectedbetween VDD and the terminal 1411 of the first PMOS transistor 401opposite the common node 495. Also, the pull down logic 1403 is definedby NMOS transistor 1403A connected between GND and the terminal 1413 ofthe second NMOS transistor 405 opposite the common node 495. Respectivegates of the PMOS transistor 1401A and NMOS transistor 1403A areconnected together at the node 1415. The pull up logic 1405 is definedby the PMOS transistor 1405A connected between the second PMOStransistor 403 and the common node 495. The pull down logic 1407 isdefined by the NMOS transistor 1407A connected between the first NMOStransistor 407 and the common node 495. Respective gates of the PMOStransistor 1405A and NMOS transistor 1407A are connected together at thenode 1421. It should be understood that the implementations of pull uplogic 1401, 1405 and pull down logic 1403, 1407 as shown in FIG. 15B areexemplary. In other embodiments, logic different than that shown in FIG.15B can be used to implement the pull up logic 1401, 1405 and the pulldown logic 1403, 1407.

FIG. 15C shows a multi-level layout of the multiplexer circuit of FIG.15B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1501, a (one-dimensional)metal-1 structure 1503, a via 1505, a (one-dimensional) metal-2structure 1507, a via 1509, a (one-dimensional) metal-1 structure 1511,and a gate contact 1513. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 1515, a (two-dimensional)metal-1 structure 1517, and a gate contact 1519. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 1521, a (one-dimensional) metal-1 structure1523, a via 1525, a (one-dimensional) metal-2 structure 1527, a via1529, a (one-dimensional) metal-1 structure 1531, and a diffusioncontact 1533. Respective gates of the PMOS transistor 1401A and NMOStransistor 1403A are connected to the node 1415 by a gate contact 1535.Also, respective gates of the PMOS transistor 1405A and NMOS transistor1407A are connected to the node 1421 by a gate contact 1539.

FIG. 16A shows a generalized multiplexer circuit in which thecross-coupled transistors (401, 403, 405, 407) are connected to form twotransmission gates 1602, 1604 to the common node 495, in accordance withone embodiment of the present invention. As previously discussed, gatesof the first PMOS transistor 401 and first NMOS transistor 407 areelectrically connected, as shown by electrical connection 491. Also,gates of the second PMOS transistor 403 and second NMOS transistor 405are electrically connected, as shown by electrical connection 493. Thefirst PMOS transistor 401 and second NMOS transistor 405 are connectedto form a first transmission gate 1602 to the common node 495. Thesecond PMOS transistor 403 and first NMOS transistor 407 are connectedto form a second transmission gate 1604 to the common node 495. Drivinglogic 1601 is electrically connected to both the first PMOS transistor401 and second NMOS transistor 405 at a terminal opposite the commonnode 495. Driving logic 1603 is electrically connected to both thesecond PMOS transistor 403 and first NMOS transistor 407 at a terminalopposite the common node 495.

FIG. 16B shows an exemplary implementation of the multiplexer circuit ofFIG. 16A with a detailed view of the driving logic 1601 and 1603, inaccordance with one embodiment of the present invention. In theembodiment of FIG. 16B, the driving logic 1601 is defined by an inverter1601A and, the driving logic 1603 is defined by an inverter 1603A.However, it should be understood that in other embodiments, the drivinglogic 1601 and 1603 can be defined by any logic function, such as a twoinput NOR gate, a two input NAND gate, AND-OR logic, OR-AND logic, amongothers, by way of example.

FIG. 16C shows a multi-level layout of the multiplexer circuit of FIG.16B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1619, a (two-dimensional)metal-1 structure 1621, and a gate contact 1623. The electricalconnection 493 between the gate electrode 403A of the second PMOStransistor 403 and the gate electrode 405A of the second NMOS transistor405 is formed by a multi-level connection that includes a gate contact1605, a (one-dimensional) metal-1 structure 1607, a via 1609, a(one-dimensional) metal-2 structure 1611, a via 1613, a(one-dimensional) metal-1 structure 1615, and a gate contact 1617. Thecommon node electrical connection 495 is formed by a multi-levelconnection that includes a diffusion contact 1625, a (one-dimensional)metal-1 structure 1627, a via 1629, a (one-dimensional) metal-2structure 1631, a via 1633, a (one-dimensional) metal-1 structure 1635,and a diffusion contact 1637. Transistors which form the inverter 1601Aare shown within the region bounded by the dashed line 1601AL.Transistors which form the inverter 1603A are shown within the regionbounded by the dashed line 1603AL.

FIG. 17A shows a generalized multiplexer circuit in which twotransistors (403, 407) of the four cross-coupled transistors areconnected to form a transmission gate 1702 to the common node 495, inaccordance with one embodiment of the present invention. As previouslydiscussed, gates of the first PMOS transistor 401 and first NMOStransistor 407 are electrically connected, as shown by electricalconnection 491. Also, gates of the second PMOS transistor 403 and secondNMOS transistor 405 are electrically connected, as shown by electricalconnection 493. The second PMOS transistor 403 and first NMOS transistor407 are connected to form the transmission gate 1702 to the common node495. Driving logic 1701 is electrically connected to both the secondPMOS transistor 403 and first NMOS transistor 407 at a terminal oppositethe common node 495. Pull up driving logic 1703 is electricallyconnected to the first PMOS transistor 401 at a terminal opposite thecommon node 495. Also, pull down driving logic 1705 is electricallyconnected to the second NMOS transistor 405 at a terminal opposite thecommon node 495.

FIG. 17B shows an exemplary implementation of the multiplexer circuit ofFIG. 17A with a detailed view of the driving logic 1701, 1703, and 1705,in accordance with one embodiment of the present invention. The drivinglogic 1701 is defined by an inverter 1701A. The pull up driving logic1703 is defined by a PMOS transistor 1703A connected between VDD and thefirst PMOS transistor 401. The pull down driving logic 1705 is definedby an NMOS transistor 1705A connected between GND and the second NMOStransistor 405. Respective gates of the PMOS transistor 1703A and NMOStransistor 1705A are connected together at the node 1707. It should beunderstood that the implementations of driving logic 1701, 1703, and1705, as shown in FIG. 17B are exemplary. In other embodiments, logicdifferent than that shown in FIG. 17B can be used to implement thedriving logic 1701, 1703, and 1705.

FIG. 17C shows a multi-level layout of the multiplexer circuit of FIG.17B implemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1723, a (two-dimensional)metal-1 structure 1725, and a gate contact 1727. The electricalconnection 493 between the gate electrode 403A of the second PMOStransistor 403 and the gate electrode 405A of the second NMOS transistor405 is formed by a multi-level connection that includes a gate contact1709, a (one-dimensional) metal-1 structure 1711, a via 1713, a(one-dimensional) metal-2 structure 1715, a via 1717, a(one-dimensional) metal-1 structure 1719, and a gate contact 1721. Thecommon node electrical connection 495 is formed by a multi-levelconnection that includes a diffusion contact 1729, a (one-dimensional)metal-1 structure 1731, a via 1733, a (one-dimensional) metal-2structure 1735, a via 1737, a (one-dimensional) metal-1 structure 1739,and a diffusion contact 1741. Transistors which form the inverter 1701Aare shown within the region bounded by the dashed line 1701AL.Respective gates of the PMOS transistor 1703A and NMOS transistor 1705Aare connected to the node 1707 by a gate contact 1743.

Example Latch Embodiments

FIG. 18A shows a generalized latch circuit implemented using thecross-coupled transistor configuration, in accordance with oneembodiment of the present invention. The gates of the first PMOStransistor 401 and first NMOS transistor 407 are electrically connected,as shown by electrical connection 491. The gates of the second PMOStransistor 403 and second NMOS transistor 405 are electricallyconnected, as shown by electrical connection 493. Each of the fourcross-coupled transistors are electrically connected to the common node495. It should be understood that the common node 495 serves as astorage node in the latch circuit. Pull up driver logic 1805 iselectrically connected to the second PMOS transistor 403 at a terminalopposite the common node 495. Pull down driver logic 1807 iselectrically connected to the first NMOS transistor 407 at a terminalopposite the common node 495. Pull up feedback logic 1809 iselectrically connected to the first PMOS transistor 401 at a terminalopposite the common node 495. Pull down feedback logic 1811 iselectrically connected to the second NMOS transistor 405 at a terminalopposite the common node 495. Additionally, the common node 495 isconnected to an input of an inverter 1801. An output of the inverter1801 is electrically connected to a feedback node 1803. It should beunderstood that in other embodiments the inverter 1801 can be replacedby any logic function, such as a two input NOR gate, a two input NANDgate, among others, or any complex logic function.

FIG. 18B shows an exemplary implementation of the latch circuit of FIG.18A with a detailed view of the pull up driver logic 1805, the pull downdriver logic 1807, the pull up feedback logic 1809, and the pull downfeedback logic 1811, in accordance with one embodiment of the presentinvention. The pull up driver logic 1805 is defined by a PMOS transistor1805A connected between VDD and the second PMOS transistor 403 oppositethe common node 495. The pull down driver logic 1807 is defined by anNMOS transistor 1807A connected between GND and the first NMOStransistor 407 opposite the common node 495. Respective gates of thePMOS transistor 1805A and NMOS transistor 1807A are connected togetherat anode 1804. The pull up feedback logic 1809 is defined by a PMOStransistor 1809A connected between VDD and the first PMOS transistor 401opposite the common node 495. The pull down feedback logic 1811 isdefined by an NMOS transistor 1811A connected between GND and the secondNMOS transistor 405 opposite the common node 495. Respective gates ofthe PMOS transistor 1809A and NMOS transistor 1811A are connectedtogether at the feedback node 1803. It should be understood that theimplementations of pull up driver logic 1805, pull down driver logic1807, pull up feedback logic 1809, and pull down feedback logic 1811 asshown in FIG. 18B are exemplary. In other embodiments, logic differentthan that shown in FIG. 18B can be used to implement the pull up driverlogic 1805, the pull down driver logic 1807, the pull up feedback logic1809, and the pull down feedback logic 1811.

FIG. 18C shows a multi-level layout of the latch circuit of FIG. 18Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1813, a (one-dimensional)metal-1 structure 1815, a via 1817, a (one-dimensional) metal-2structure 1819, a via 1821, a (one-dimensional) metal-1 structure 1823,and a gate contact 1825. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 1827, a (two-dimensional)metal-1 structure 1829, and a gate contact 1831. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 1833, a (one-dimensional) metal-1 structure1835, a via 1837, a (one-dimensional) metal-2 structure 1839, a via1841, a (two-dimensional) metal-1 structure 1843, and a diffusioncontact 1845. Transistors which form the inverter 1801 are shown withinthe region bounded by the dashed line 1801L.

FIG. 19A shows the latch circuit of FIG. 18A in which the twocross-coupled transistors 401 and 405 remain directly connected to theoutput node 495, and in which the two cross-coupled transistors 403 and407 are positioned outside the pull up driver logic 1805 and pull downdriver logic 1807, respectively, relative to the common node 495, inaccordance with one embodiment of the present invention. Pull up driverlogic 1805 is electrically connected between the second PMOS transistor403 and the common node 495. Pull down driver logic 1807 is electricallyconnected between the first NMOS transistor 407 and the common node 495.With the exception of repositioning the PMOS/NMOS transistors 403/407outside of their pull up/down driver logic 1805/1807 relative to thecommon node 495, the circuit of FIG. 19A is the same as the circuit ofFIG. 18A.

FIG. 19B shows an exemplary implementation of the latch circuit of FIG.19A with a detailed view of the pull up driver logic 1805, pull downdriver logic 1807, pull up feedback logic 1809, and pull down feedbacklogic 1811, in accordance with one embodiment of the present invention.As previously discussed with regard to FIG. 18B, the pull up feedbacklogic 1809 is defined by the PMOS transistor 1809A connected between VDDand the first PMOS transistor 401 opposite the common node 495. Also,the pull down feedback logic 1811 is defined by NMOS transistor 1811Aconnected between GND and the second NMOS transistor 405 opposite thecommon node 495. Respective gates of the PMOS transistor 1809A and NMOStransistor 1811A are connected together at the feedback node 1803. Thepull up driver logic 1805 is defined by the PMOS transistor 1805Aconnected between the second PMOS transistor 403 and the common node495. The pull down driver logic 1807 is defined by the NMOS transistor1807A connected between the first NMOS transistor 407 and the commonnode 495. Respective gates of the PMOS transistor 1805A and NMOStransistor 1807A are connected together at the node 1804. It should beunderstood that the implementations of pull up driver logic 1805, pulldown driver logic 1807, pull up feedback logic 1809, and pull downfeedback logic 1811 as shown in FIG. 19B are exemplary. In otherembodiments, logic different than that shown in FIG. 19B can be used toimplement the pull up driver logic 1805, the pull down driver logic1807, the pull up feedback logic 1809, and the pull down feedback logic1811.

FIG. 19C shows a multi-level layout of the latch circuit of FIG. 19Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 1901, a (one-dimensional)metal-1 structure 1903, a via 1905, a (one-dimensional) metal-2structure 1907, a via 1909, a (one-dimensional) metal-1 structure 1911,and a gate contact 1913. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 1915, a (two-dimensional)metal-1 structure 1917, and a gate contact 1919. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 1921, a (one-dimensional) metal-1 structure1923, a via 1925, a (one-dimensional) metal-2 structure 1927, a via1929, a (two-dimensional) metal-1 structure 1931, and a diffusioncontact 1933. Transistors which form the inverter 1801 are shown withinthe region bounded by the dashed line 1801L.

FIG. 20A shows the latch circuit of FIG. 18A in which the twocross-coupled transistors 403 and 407 remain directly connected to theoutput node 495, and in which the two cross-coupled transistors 401 and405 are positioned outside the pull up feedback logic 1809 and pull downfeedback logic 1811, respectively, relative to the common node 495, inaccordance with one embodiment of the present invention. Pull upfeedback logic 1809 is electrically connected between the first PMOStransistor 401 and the common node 495. Pull down feedback logic 1811 iselectrically connected between the second NMOS transistor 405 and thecommon node 495. With the exception of repositioning the PMOS/NMOStransistors 401/405 outside of their pull up/down feedback logic1809/1811 relative to the common node 495, the circuit of FIG. 20A isthe same as the circuit of FIG. 18A.

FIG. 20B shows an exemplary implementation of the latch circuit of FIG.20A with a detailed view of the pull up driver logic 1805, pull downdriver logic 1807, pull up feedback logic 1809, and pull down feedbacklogic 1811, in accordance with one embodiment of the present invention.The pull up feedback logic 1809 is defined by the PMOS transistor 1809Aconnected between the first PMOS transistor 401 and the common node 495.Also, the pull down feedback logic 1811 is defined by NMOS transistor1811A connected between the second NMOS transistor 405 and the commonnode 495. Respective gates of the PMOS transistor 1809A and NMOStransistor 1811A are connected together at the feedback node 1803. Thepull up driver logic 1805 is defined by the PMOS transistor 1805Aconnected between VDD and the second PMOS transistor 403. The pull downdriver logic 1807 is defined by the NMOS transistor 1807A connectedbetween GND and the first NMOS transistor 407. Respective gates of thePMOS transistor 1805A and NMOS transistor 1807A are connected togetherat the node 1804. It should be understood that the implementations ofpull up driver logic 1805, pull down driver logic 1807, pull up feedbacklogic 1809, and pull down feedback logic 1811 as shown in FIG. 20B areexemplary. In other embodiments, logic different than that shown in FIG.20B can be used to implement the pull up driver logic 1805, the pulldown driver logic 1807, the pull up feedback logic 1809, and the pulldown feedback logic 1811.

FIG. 20C shows a multi-level layout of the latch circuit of FIG. 20Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 2001, a (one-dimensional)metal-1 structure 2003, a via 2005, a (one-dimensional) metal-2structure 2007, a via 2009, a (one-dimensional) metal-1 structure 2011,and a gate contact 2013. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 2015, a (one-dimensional)metal-1 structure 2017, and a gate contact 2019. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 2021, a (two-dimensional) metal-1 structure2023, and a diffusion contact 2025. Transistors which form the inverter1801 are shown within the region bounded by the dashed line 1801L.

FIG. 21A shows a generalized latch circuit in which the cross-coupledtransistors (401, 403, 405, 407) are connected to form two transmissiongates 2103, 2105 to the common node 495, in accordance with oneembodiment of the present invention. As previously discussed, gates ofthe first PMOS transistor 401 and first NMOS transistor 407 areelectrically connected, as shown by electrical connection 491. Also,gates of the second PMOS transistor 403 and second NMOS transistor 405are electrically connected, as shown by electrical connection 493. Thefirst PMOS transistor 401 and second NMOS transistor 405 are connectedto form a first transmission gate 2103 to the common node 495. Thesecond PMOS transistor 403 and first NMOS transistor 407 are connectedto form a second transmission gate 2105 to the common node 495. Feedbacklogic 2109 is electrically connected to both the first PMOS transistor401 and second NMOS transistor 405 at a terminal opposite the commonnode 495. Driving logic 2107 is electrically connected to both thesecond PMOS transistor 403 and first NMOS transistor 407 at a terminalopposite the common node 495. Additionally, the common node 495 isconnected to the input of the inverter 1801. The output of the inverter1801 is electrically connected to a feedback node 2101. It should beunderstood that in other embodiments the inverter 1801 can be replacedby any logic function, such as a two input NOR gate, a two input NANDgate, among others, or any complex logic function.

FIG. 21B shows an exemplary implementation of the latch circuit of FIG.21A with a detailed view of the driving logic 2107 and feedback logic2109, in accordance with one embodiment of the present invention. Thedriving logic 2107 is defined by an inverter 2107A. Similarly, thefeedback logic 2109 is defined by an inverter 2109A. It should beunderstood that in other embodiments, the driving logic 2107 and/or 2109can be defined by logic other than an inverter.

FIG. 21C shows a multi-level layout of the latch circuit of FIG. 21Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 2111, a (one-dimensional)metal-1 structure 2113, a via 2115, a (one-dimensional) metal-2structure 2117, a via 2119, a (one-dimensional) metal-1 structure 2121,and a gate contact 2123. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 2125, a (two-dimensional)metal-1 structure 2127, and a gate contact 2129. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 2131, a (one-dimensional) metal-1 structure2133, a via 2135, a (one-dimensional) metal-2 structure 2137, a via2139, a (two-dimensional) metal-1 structure 2141, and a diffusioncontact 2143. Transistors which form the inverter 2107A are shown withinthe region bounded by the dashed line 2107AL. Transistors which form theinverter 2109A are shown within the region bounded by the dashed line2109AL. Transistors which form the inverter 1801 are shown within theregion bounded by the dashed line 1801L.

FIG. 22A shows a generalized latch circuit in which two transistors(403, 407) of the four cross-coupled transistors are connected to form atransmission gate 2105 to the common node 495, in accordance with oneembodiment of the present invention. As previously discussed, gates ofthe first PMOS transistor 401 and first NMOS transistor 407 areelectrically connected, as shown by electrical connection 491. Also,gates of the second PMOS transistor 403 and second NMOS transistor 405are electrically connected, as shown by electrical connection 493. Thesecond PMOS transistor 403 and first NMOS transistor 407 are connectedto form the transmission gate 2105 to the common node 495. Driving logic2201 is electrically connected to both the second PMOS transistor 403and first NMOS transistor 407 at a terminal opposite the common node495. Pull up feedback logic 2203 is electrically connected to the firstPMOS transistor 401 at a terminal opposite the common node 495. Also,pull down feedback logic 2205 is electrically connected to the secondNMOS transistor 405 at a terminal opposite the common node 495.

FIG. 22B shows an exemplary implementation of the latch circuit of FIG.22A with a detailed view of the driving logic 2201, the pull up feedbacklogic 2203, and the pull down feedback logic 2205, in accordance withone embodiment of the present invention. The driving logic 2201 isdefined by an inverter 2201A. The pull up feedback logic 2203 is definedby a PMOS transistor 2203A connected between VDD and the first PMOStransistor 401. The pull down feedback logic 2205 is defined by an NMOStransistor 2205A connected between GND and the second NMOS transistor405. Respective gates of the PMOS transistor 2203A and NMOS transistor2205A are connected together at the feedback node 2101. It should beunderstood that in other embodiments, the driving logic 2201 can bedefined by logic other than an inverter. Also, it should be understoodthat in other embodiments, the pull up feedback logic 2203 and/or pulldown feedback logic 2205 can be defined logic different than what isshown in FIG. 22B.

FIG. 22C shows a multi-level layout of the latch circuit of FIG. 22Bimplemented using a restricted gate level layout architecturecross-coupled transistor layout, in accordance with one embodiment ofthe present invention. The electrical connection 491 between the gateelectrode 401A of the first PMOS transistor 401 and the gate electrode407A of the first NMOS transistor 407 is formed by a multi-levelconnection that includes a gate contact 2207, a (one-dimensional)metal-1 structure 2209, a via 2211, a (one-dimensional) metal-2structure 2213, a via 2215, a (one-dimensional) metal-1 structure 2217,and a gate contact 2219. The electrical connection 493 between the gateelectrode 403A of the second PMOS transistor 403 and the gate electrode405A of the second NMOS transistor 405 is formed by a multi-levelconnection that includes a gate contact 2221, a (two-dimensional)metal-1 structure 2223, and a gate contact 2225. The common nodeelectrical connection 495 is formed by a multi-level connection thatincludes a diffusion contact 2227, a (one-dimensional) metal-1 structure2229, a via 2231, a (one-dimensional) metal-2 structure 2233, a via2235, a (two-dimensional) metal-1 structure 2237, and a diffusioncontact 2239. Transistors which form the inverter 2201A are shown withinthe region bounded by the dashed line 2201AL. Transistors which form theinverter 1801 are shown within the region bounded by the dashed line1801L.

Exemplary Embodiments

In one embodiment, a cross-coupled transistor configuration is definedwithin a semiconductor chip. This embodiment is illustrated in part withregard to FIG. 2. In this embodiment, a first P channel transistor (401)is defined to include a first gate electrode (401A) defined in a gatelevel of the chip. Also, a first N channel transistor (407) is definedto include a second gate electrode (407A) defined in the gate level ofthe chip. The second gate electrode (407A) of the first N channeltransistor (407) is electrically connected to the first gate electrode(401A) of the first P channel transistor (401). Further, a second Pchannel transistor (403) is defined to include a third gate electrode(403A) defined in the gate level of a chip. Also, a second N channeltransistor (405) is defined to include a fourth gate electrode (405A)defined in the gate level of the chip. The fourth gate electrode (405A)of the second N channel transistor (405) is electrically connected tothe third gate electrode (403A) of the second P channel transistor(403). Additionally, each of the first P channel transistor (401), firstN channel transistor (407), second P channel transistor (403), andsecond N channel transistor (405) has a respective diffusion terminalelectrically connected to a common node (495).

It should be understood that in some embodiments, one or more of thefirst P channel transistor (401), the first N channel transistor (407),the second P channel transistor (403), and the second N channeltransistor (405) can be respectively implemented by a number oftransistors electrically connected in parallel. In this instance, thetransistors that are electrically connected in parallel can beconsidered as one device corresponding to either of the first P channeltransistor (401), the first N channel transistor (407), the second Pchannel transistor (403), and the second N channel transistor (405). Itshould be understood that electrical connection of multiple transistorsin parallel to form a given transistor of the cross-coupled transistorconfiguration can be utilized to achieve a desired drive strength forthe given transistor.

In one embodiment, each of the first (401A), second (407A), third(403A), and fourth (405A) gate electrodes is defined to extend along anyof a number of gate electrode tracks, such as described with regard toFIG. 3. The number of gate electrode tracks extend across the gate levelof the chip in a parallel orientation with respect to each other. Also,it should be understood that each of the first (401A), second (407A),third (403A), and fourth (405A) gate electrodes corresponds to a portionof a respective gate level feature defined within a gate level featurelayout channel. Each gate level feature is defined within its gate levelfeature layout channel without physically contacting another gate levelfeature defined within an adjoining gate level feature layout channel.Each gate level feature layout channel is associated with a given gateelectrode track and corresponds to a layout region that extends alongthe given gate electrode track and perpendicularly outward in eachopposing direction from the given gate electrode track to a closest ofeither an adjacent gate electrode track or a virtual gate electrodetrack outside a layout boundary, such as described with regard to FIG.3B.

In various implementations of the above-described embodiment, such as inthe exemplary layouts of FIGS. 10, 11, 14C, 15C, 16C, 17C, 18C, 19C,20C, 21C, 22C, the second gate electrode (407A) is electricallyconnected to the first gate electrode (401A) through at least oneelectrical conductor defined within any chip level other than the gatelevel. And, the fourth gate electrode (405A) is electrically connectedto the third gate electrode (403A) through at least one electricalconductor defined within any chip level other than the gate level.

In various implementations of the above-described embodiment, such as inthe exemplary layout of FIG. 13, both the second gate electrode (407A)and the first gate electrode (401A) are formed from a single gate levelfeature that is defined within a same gate level feature layout channelthat extends along a single gate electrode track over both a p typediffusion region and an n type diffusion region. And, the fourth gateelectrode (405A) is electrically connected to the third gate electrode(403A) through at least one electrical conductor defined within any chiplevel other than the gate level.

In various implementations of the above-described embodiment, such as inthe exemplary layouts of FIG. 12, both the second gate electrode (407A)and the first gate electrode (401A) are formed from a first gate levelfeature that is defined within a first gate level feature layout channelthat extends along a first gate electrode track over both a p typediffusion region and an n type diffusion region. And, both the fourthgate electrode (405A) and the third gate electrode (403A) are formedfrom a second gate level feature that is defined within a second gatelevel feature layout channel that extends along a second gate electrodetrack over both a p type diffusion region and an n type diffusionregion.

In one embodiment, the above-described gate electrode cross-coupledtransistor configuration is used to implement a multiplexer having notransmission gates. This embodiment is illustrated in part with regardto FIGS. 14-15. In this embodiment, a first configuration of pull-uplogic (1401) is electrically connected to the first P channel transistor(401), a first configuration of pull-down logic (1407) electricallyconnected to the first N channel transistor (407), a secondconfiguration of pull-up logic (1405) electrically connected to thesecond P channel transistor (403), and a second configuration ofpull-down logic (1403) electrically connected to the second N channeltransistor (405).

In the particular embodiments of FIGS. 14B and 15B, the firstconfiguration of pull-up logic (1401) is defined by a third P channeltransistor (1401A), and the second configuration of pull-down logic(1403) is defined by a third N channel transistor (1403A). Respectivegates of the third P channel transistor (1401A) and third N channeltransistor (1403A) are electrically connected together so as to receivea substantially equivalent electrical signal. Moreover, the firstconfiguration of pull-down logic (1407) is defined by a fourth N channeltransistor (1407A), and the second configuration of pull-up logic (1405)is defined by a fourth P channel transistor (1405A). Respective gates ofthe fourth P channel transistor (1405A) and fourth N channel transistor(1407A) are electrically connected together so as to receive asubstantially equivalent electrical signal.

In one embodiment, the above-described gate electrode cross-coupledtransistor configuration is used to implement a multiplexer having onetransmission gate. This embodiment is illustrated in part with regard toFIG. 17. In this embodiment, a first configuration of pull-up logic(1703) is electrically connected to the first P channel transistor(401), a first configuration of pull-down logic (1705) electricallyconnected to the second N channel transistor (405), and mux drivinglogic (1701) is electrically connected to both the second P channeltransistor (403) and the first N channel transistor (407).

In the exemplary embodiment of FIG. 17B, the first configuration ofpull-up logic (1703) is defined by a third P channel transistor (1703A),and the first configuration of pull-down logic (1705) is defined by athird N channel transistor (1705A). Respective gates of the third Pchannel transistor (1703A) and third N channel transistor (1705A) areelectrically connected together so as to receive a substantiallyequivalent electrical signal. Also, the mux driving logic (1701) isdefined by an inverter (1701A).

In one embodiment, the above-described gate electrode cross-coupledtransistor configuration is used to implement a latch having notransmission gates. This embodiment is illustrated in part with regardto FIGS. 18-20. In this embodiment, pull-up driver logic (1805) iselectrically connected to the second P channel transistor (403),pull-down driver logic (1807) is electrically connected to the first Nchannel transistor (407), pull-up feedback logic (1809) is electricallyconnected to the first P channel transistor (401), and pull-downfeedback logic (1811) is electrically connected to the second N channeltransistor (405). Also, the latch includes an inverter (1801) having aninput connected to the common node (495) and an output connected to afeedback node (1803). Each of the pull-up feedback logic (1809) andpull-down feedback logic (1811) is connected to the feedback node(1803).

In the exemplary embodiments of FIGS. 18B, 19B, and 20B, the pull-updriver logic (1805) is defined by a third P channel transistor (1805A),and the pull-down driver logic (1807) is defined by a third N channeltransistor (1807A). Respective gates of the third P channel transistor(1805A) and third N channel transistor (1807A) are electricallyconnected together so as to receive a substantially equivalentelectrical signal. Additionally, the pull-up feedback logic (1809) isdefined by a fourth P channel transistor (1809A), and the pull-downfeedback logic (1811) is defined by a fourth N channel transistor(1811A). Respective gates of the fourth P channel transistor (1809A) andfourth N channel transistor (1811A) are electrically connected togetherat the feedback node (1803).

In one embodiment, the above-described gate electrode cross-coupledtransistor configuration is used to implement a latch having twotransmission gates. This embodiment is illustrated in part with regardto FIG. 21. In this embodiment, driving logic (2107) is electricallyconnected to both the second P channel transistor (403) and the first Nchannel transistor (407). Also, feedback logic (2109) is electricallyconnected to both the first P channel transistor (401) and the second Nchannel transistor (405). The latch further includes a first inverter(1801) having an input connected to the common node (495) and an outputconnected to a feedback node (2101). The feedback logic (2109) iselectrically connected to the feedback node (2101). In the exemplaryembodiment of FIG. 21B, the driving logic (2107) is defined by a secondinverter (2107A), and the feedback logic (2109) is defined by a thirdinverter (2109A).

In one embodiment, the above-described gate electrode cross-coupledtransistor configuration is used to implement a latch having onetransmission gate. This embodiment is illustrated in part with regard toFIG. 22. In this embodiment, driving logic (2201) is electricallyconnected to both the second P channel transistor (403) and the first Nchannel transistor (407). Also, pull up feedback logic (2203) iselectrically connected to the first P channel transistor (401), and pulldown feedback logic (2205) electrically connected to the second Nchannel transistor (405). The latch further includes a first inverter(1801) having an input connected to the common node (495) and an outputconnected to a feedback node (2101). Both the pull up feedback logic(2203) and pull down feedback logic (2205) are electrically connected tothe feedback node (2101). In the exemplary embodiment of FIG. 22B, thedriving logic (2201) is defined by a second inverter (2201A). Also, thepull up feedback logic (2203) is defined by a third P channel transistor(2203A) electrically connected between the first P channel transistor(401) and the feedback node (2101). The pull down feedback logic (2205)is defined by a third N channel transistor (2205A) electricallyconnected between the second N channel transistor (405) and the feedbacknode (2101).

In one embodiment, cross-coupled transistors devices are defined andconnected to form part of an integrated circuit within a semiconductorchip (“chip” hereafter). The chip includes a number of levels withinwhich different features are defined to form the integrated circuit andcross-coupled transistors therein. The chip includes a substrate withinwhich a number of diffusion regions are formed. The chip also includes agate level in which a number of gate electrodes are formed. The chipfurther includes a number of interconnect levels successively definedabove the gate level. A dielectric material is used to electricallyseparate a given level from its vertically adjacent levels. A number ofcontact features are defined to extend vertically through the chip toconnect gate electrode features and diffusion regions, respectively, tovarious interconnect level features. Also, a number of via features aredefined to extend vertically through the chip to connect variousinterconnect level features.

The gate level of the various embodiments disclosed herein is defined asa linear gate level and includes a number of commonly oriented lineargate level features. Some of the linear gate level features form gateelectrodes of transistor devices. Others of the linear gate levelfeatures can form conductive segments extending between two pointswithin the gate level. Also, others of the linear gate level featuresmay be non-functional with respect to integrated circuit operation. Itshould be understood that the each of the linear gate level features,regardless of function, is defined to extend across the gate level in acommon direction and to be devoid of a substantial change in directionalong its length. Therefore, each of the gate level features is definedto be parallel to each other when viewed from a perspectiveperpendicular to the gate level.

It should be understood that each of the linear gate electrode features,regardless of function, is defined such that no linear gate electrodefeature along a given line of extent is configured to connect directlywithin the gate electrode level to another linear gate electrode featuredefined along another parallel line of extent, without utilizing anon-gate electrode feature. Moreover, each connection between lineargate electrode features that are placed on different, yet parallel,lines of extent is made through one or more non-gate electrode features,which may be defined in higher interconnect level(s), i.e., through oneor more interconnect level(s) above the gate electrode level, or by wayof local interconnect features within the linear gate level. In oneembodiment, the linear gate electrode features are placed according to avirtual grid or virtual grate. However, it should be understood that inother embodiments the linear gate electrode features, although orientedto have a common direction of extent, are placed without regard to avirtual grid or virtual grate.

Additionally, it should be understood that while each linear gateelectrode feature is defined to be devoid of a substantial change indirection along its line of extent, each linear gate electrode featuremay have one or more contact head portion(s) defined at any number oflocation(s) along its length. A contact head portion of a given lineargate electrode feature is defined as a segment of the linear gateelectrode feature having a different width than a gate portion of thelinear gate electrode feature, i.e., than a portion of the linear gateelectrode feature that extends over a diffusion region, wherein “width”is defined across the substrate in a direction perpendicular to the lineof extent of the given linear gate electrode feature. It should beappreciated that a contact head of linear gate electrode feature, whenviewed from above, can be defined by essentially any rectangular layoutshape, including a square and a rectangle. Also, depending on layoutrequirements and circuit design, a given contact head portion of alinear gate electrode feature may or may not have a gate contact definedthereabove.

In one embodiment, a substantial change in direction of a linear gatelevel feature exists when the width of the linear gate level feature atany point thereon changes by more than 50% of the nominal width of thelinear gate level feature along its entire length. In anotherembodiment, a substantial change in direction of a linear gate levelfeature exists when the width of the linear gate level feature changesfrom any first location on the linear gate level feature to any secondlocation on the linear gate level feature by more that 50% of the lineargate level feature width at the first location. Therefore, it should beappreciated that the use of non-linear-shaped gate level features isspecifically avoided, wherein a non-linear-shaped gate level featureincludes one or more significant bends within a plane of the gate level.

Each of the linear gate level features has a width defined perpendicularto its direction of extent across the gate level. In one embodiment, thevarious gate level features can be defined to have different widths. Inanother embodiment, the various gate level features can be defined tohave the same width. Also, a center-to-center spacing between adjacentlinear gate level features, as measured perpendicular to their directionof extent across the gate level, is referred to as gate pitch. In oneembodiment, a uniform gate pitch is used. However, in anotherembodiment, the gate pitch can vary across the gate level. It should beunderstood that linear gate level feature width and pitch specificationscan be established for a portion of the chip and can be different forseparate portions of the chip, wherein the portion of the chip may be ofany size and shape.

Various embodiments are disclosed herein for cross-coupled transistorlayouts defined using the linear gate level as described above. Eachcross-coupled transistor layout embodiment includes four cross-coupledtransistors, wherein each of these four cross-coupled transistors isdefined in part by a respective linear gate electrode feature, andwherein the linear gate electrode features of the cross-coupledtransistors are oriented to extend across the layout in a parallelrelationship to each other.

Also, in each cross-coupled transistor layout, each of the gateelectrodes of the four cross-coupled transistors is associated with,i.e., electrically interfaced with, a respective diffusion region. Thediffusion regions associated with the gate electrodes of thecross-coupled transistors are electrically connected to a common node.In various embodiments, connection of the cross-coupled transistor'sdiffusion regions to the common node can be made in many different ways.

For example, in one embodiment, two PMOS transistors of thecross-coupled transistors are disposed over a common p-type diffusionregion, two NMOS transistors of the cross-coupled transistors aredisposed over a common n-type diffusion region, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node. FIGS. 26-99, 150-157, and168-172 illustrate various cross-coupled transistor layout embodimentsin which two PMOS transistors of the cross-coupled transistors aredisposed over a common p-type diffusion region, two NMOS transistors ofthe cross-coupled transistors are disposed over a common n-typediffusion region, and the p-type and n-type diffusion regions associatedwith the cross-coupled transistors are electrically connected to acommon node. It should be understood that although FIGS. 26-99 do notexplicitly show an electrical connection of the n-type and p-typediffusion regions of the cross-coupled transistors to a common node,this common node connection between the n-type and p-type diffusionregions of the cross-coupled transistors is present in a full version ofthe exemplary layouts.

In another embodiment, two PMOS transistors of the cross-coupledtransistors are respectively disposed over physically separated p-typediffusion regions, two NMOS transistors of the cross-coupled transistorsare disposed over a common n-type diffusion region, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node. FIGS. 103, 105, 112-149,167, 184, and 186 illustrate various cross-coupled transistor layoutembodiments in which two PMOS transistors of the cross-coupledtransistors are respectively disposed over physically separated p-typediffusion regions, two NMOS transistors of the cross-coupled transistorsare disposed over a common n-type diffusion region, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node.

In another embodiment, two PMOS transistors of the cross-coupledtransistors are disposed over a common p-type diffusion region, two NMOStransistors of the cross-coupled transistors are respectively disposedover physically separated n-type diffusion regions, and the p-type andn-type diffusion regions associated with the cross-coupled transistorsare electrically connected to a common node. FIG. 100 as shown and eachof FIGS. 103, 105, 112-149, 167, 184, and 186 with the p-type and n-typediffusion regions reversed to n-type and p-type, respectively,illustrate various cross-coupled transistor layout embodiments in whichtwo PMOS transistors of the cross-coupled transistors are disposed overa common p-type diffusion region, two NMOS transistors of thecross-coupled transistors are respectively disposed over physicallyseparated n-type diffusion regions, and the p-type and n-type diffusionregions associated with the cross-coupled transistors are electricallyconnected to a common node.

In yet another embodiment, two PMOS transistors of the cross-coupledtransistors are respectively disposed over physically separated p-typediffusion regions, two NMOS transistors of the cross-coupled transistorsare respectively disposed over physically separated n-type diffusionregions, and the p-type and n-type diffusion regions associated with thecross-coupled transistors are electrically connected to a common node.FIGS. 158-166, 173-183, 185, and 187-191 illustrate variouscross-coupled transistor layout embodiments in which two PMOStransistors of the cross-coupled transistors are respectively disposedover physically separated p-type diffusion regions, two NMOS transistorsof the cross-coupled transistors are respectively disposed overphysically separated n-type diffusion regions, and the p-type and n-typediffusion regions associated with the cross-coupled transistors areelectrically connected to a common node.

It should be understood that the electrical connection of the variousp-type and n-type diffusion regions associated with the cross-coupledtransistors to the common node can be made using electrical conductorsdefined within any level of the chip and within any number of levels ofthe chip, by way of contact and/or vias, so as to accommodateessentially any cross-coupled layout configuration defined in accordancewith the linear gate level restrictions. In one embodiment, electricalconnection of the diffusion regions of the cross-coupled transistors tothe common node can be made using one or more local interconnectconductors defined within the gate level itself. This embodiment mayalso combine local interconnect conductors with conductors in higherlevels (above the linear gate level) by way of contacts and/or vias tomake the electrical connection of the diffusion regions of thecross-coupled transistors to the common node. Additionally, in variousembodiments, conductive paths used to electrically connect the diffusionregions of the cross-coupled transistors to the common node can bedefined to traverse over essentially any area of the chip as required toaccommodate a routing solution for the chip.

Also, it should be appreciated that because the n-type and p-typediffusion regions are physically separate, and because the p-typediffusion regions for the two PMOS transistors of the cross-coupledtransistors can be physically separate, and because the n-type diffusionregions for the two NMOS transistors of the cross-coupled transistorscan be physically separate, it is possible in various embodiments tohave each of the four cross-coupled transistors disposed at arbitrarylocations in the layout relative to each other. Therefore, unlessnecessitated by electrical performance or other layout influencingconditions, it is not required that the four cross-coupled transistorsbe located within a prescribed proximity to each other in the layout.Although, location of the cross-coupled transistors within a prescribedproximity to each other is not precluded, and may be desirable incertain circuit layouts.

FIG. 26 is an illustration showing an exemplary cross-coupled transistorlayout, in accordance with one embodiment of the present invention. Thecross-couple layout includes four transistors 102 p, 104 p, 106 p, 108p. Transistors 102 p, 106 p are defined over a first diffusion region110 p. Transistors 108 p, 104 p are defined over a second diffusionregion 112 p. In one embodiment, the first diffusion region 110 p isdefined such that transistors 102 p and 106 p are NMOS transistors, andthe second diffusion region 112 p is defined such that transistors 104 pand 108 p are PMOS transistors. In another embodiment, the firstdiffusion region 110 p is defined such that transistors 102 p and 106 pare PMOS transistors, and the second diffusion region 112 p is definedsuch that transistors 104 p and 108 p are NMOS transistors.Additionally, the separation distance 114 p between the first and seconddiffusion regions 110 p, 112 p can vary depending on the requirements ofthe layout and the area required for connection of the cross-coupledtransistors between the first and second diffusion regions 110 p, 112 p.

In the exemplary embodiments disclosed herein, it should be understoodthat diffusion regions are not restricted in size. In other words, anygiven diffusion region can be sized in an arbitrary manner as requiredto satisfy electrical and/or layout requirements. Additionally, anygiven diffusion region can be shaped in an arbitrary manner as requiredto satisfy electrical and/or layout requirements. Additionally, asdiscussed above, in various embodiments a cross-coupled transistorconfiguration can utilize physically separate n-channel diffusionregions and/or physically separate p-channel diffusion regions. Morespecifically, the two N-MOS transistors of the cross-coupled transistorconfiguration can utilize physically separate n-channel diffusionregions, and/or the two P-MOS transistors of the cross-coupledtransistor configuration can utilize physically separate p-channeldiffusion regions.

Also, it should be understood that the four transistors of thecross-coupled transistor configuration, as defined in accordance withthe linear gate level, are not required to be the same size. Indifferent embodiments, the four transistors of the cross-coupledtransistor configuration can either vary in size (transistor width ortransistor gate length) or have the same size, depending on theapplicable electrical and/or layout requirements. Additionally, shouldbe understood that the four transistors of the cross-coupled transistorconfiguration are not required to be placed in close proximity to each,although they may be closely placed in some embodiments. Morespecifically, because connections between the transistors of thecross-coupled transistor configuration can be made by routing through asleast one higher interconnect level, there is freedom in placement ofthe four transistors of the cross-coupled transistor configurationrelative to each other. Although, it should be understood that aproximity of the four transistors of the cross-coupled transistorconfiguration may be governed in certain embodiments by electricaland/or layout optimization requirements.

The layout of FIG. 26 utilizes a linear gate level as described above.Specifically, each of linear gate level features 116Ap-116Fp, regardlessof function, is defined to extend across the gate level in a commondirection and to be devoid of a substantial change in direction alongits length. Linear gate level features 116Bp, 116Fp, 116Cp, and 116Epform the gate electrodes of transistors 102 p, 104 p, 106 p, and 108 p,respectively. The gate electrodes of transistors 106 p and 108 p areconnected through gate contacts 118 p and 120 p, and through a higherinterconnect level feature 101 p. In one embodiment, the interconnectlevel feature 101 p is a first interconnect level feature, i.e., Metal-1level feature. However, in other embodiments, the interconnect levelfeature 101 p can be a higher interconnect level feature, such as aMetal-2 level feature, or Metal-3 level feature.

In the illustrated embodiment, to facilitate fabrication (e.g.,lithographic resolution) of the interconnect level feature 101 p, edgesof the interconnect level feature 101 p are substantially aligned withedges of neighboring interconnect level features 103 p, 105 p. However,it should be understood that other embodiments may have interconnectlevel features placed without regard to interconnect level featurealignment or an interconnect level grid. Additionally, in theillustrated embodiment, to facilitate fabrication (e.g., lithographicresolution), the gate contacts 118 p and 120 p are substantially alignedwith neighboring contact features 122 p and 124 p, respectively, suchthat the gate contacts are placed according to a gate contact grid.However, it should be understood that other embodiments may have gatecontacts placed without regard to gate contact alignment or gate contactgrid.

The gate electrode of transistor 102 p is connected to the gateelectrode of transistor 104 p through gate contact 126 p, throughinterconnect level (e.g., Metal-1 level) feature 130 p, through via 132p, through higher interconnect level (e.g., Metal-2 level) feature 134p, through via 136 p, through interconnect level (e.g., Metal-1 level)feature 138 p, and through gate contacts 128 p. Although the illustratedembodiment of FIG. 26 utilizes the Metal-1 and Metal-2 levels to connectthe gate electrodes of transistors 102 p and 104 p, it should beappreciated that in various embodiment, essentially any combination ofinterconnect levels can be used to make the connection between the gateelectrodes of transistors 102 p and 104 p.

It should be appreciated that the cross-coupled transistor layout ofFIG. 26 is defined using four transistors (102 p, 104 p, 106 p, 108 p)and four gate contacts (126 p, 128 p, 118 p, 120 p). Also, the layoutembodiment of FIG. 26 can be characterized in that two of the four gatecontacts are placed between the NMOS and PMOS transistors of thecross-coupled transistors, one of the four gate contacts is placedoutside of the NMOS transistors, and one of the four gate contacts isplaced outside of the PMOS transistors. The two gate contacts placedbetween the NMOS and PMOS transistors are referred to as “inner gatecontacts.” The two gate contacts placed outside of the NMOS and PMOStransistors are referred to as “outer gate contacts.”

In describing the cross-coupled layout embodiments illustrated in thevarious Figures herein, including that of FIG. 26, the direction inwhich the linear gate level features extend across the layout isreferred to as a “vertical direction.” Correspondingly, the directionthat is perpendicular to the direction in which the linear gate levelfeatures extend across the layout is referred to as a “horizontaldirection.” With this in mind, in the cross-coupled layout of FIG. 26,it can be seen that the transistors 102 p and 104 p having the outergate contacts 126 p and 128 p, respectively, are connected by using twohorizontal interconnect level features 130 p and 138 p, and by using onevertical interconnect level feature 134 p. It should be understood thatthe horizontal and vertical interconnect level features 130 p, 134 p,138 p used to connect the outer gate contacts 126 p, 128 p can be placedessentially anywhere in the layout, i.e., can be horizontally shifted ineither direction away from the cross-coupled transistors 102 p, 104 p,106 p, 108 p, as necessary to satisfy particular layout/routingrequirements.

FIG. 27 is an illustration showing the exemplary layout of FIG. 26, withthe linear gate electrode features 116Bp, 116Cp, 116Ep, and 116Fpdefined to include contact head portions 117Bp, 117Cp, 117Ep, and 117Fp,respectively. As previously discussed, a linear gate electrode featureis allowed to have one or more contact head portion(s) along its line ofextent, so long as the linear gate electrode feature does not connectdirectly within the gate level to another linear gate electrode featurehaving a different, yet parallel, line of extent.

FIG. 28 is an illustration showing the cross-coupled transistor layoutof FIG. 26, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention. It should beunderstood that essentially any cross-coupled transistor configurationlayout defined in accordance with a linear gate level can be representedin an alternate manner by horizontally and/or vertically reversingplacement of the gate contacts that are used to connect one or bothpairs of the four transistors of the cross-coupled transistorconfiguration. Also, it should be understood that essentially anycross-coupled transistor configuration layout defined in accordance witha linear gate level can be represented in an alternate manner bymaintaining gate contact placements and by modifying each routing pathused to connect one or both pairs of the four transistors of thecross-coupled transistor configuration.

FIG. 29 is an illustration showing the cross-coupled transistor layoutof FIG. 26, with the vertical positions of the inner gate contacts 118 pand 120 p adjusted to enable alignment of the line end spacings betweenco-linearly aligned gate level features, in accordance with oneembodiment of the present invention. Specifically, gate contact 118 p isadjusted vertically upward, and gate contact 120 p is adjustedvertically downward. The linear gate level features 116Bp and 116Ep arethen adjusted such that the line end spacing 142 p therebetween issubstantially vertically centered within area shadowed by theinterconnect level feature 101 p. Similarly, the linear gate levelfeatures 116Cp and 116Fp are then adjusted such that the line endspacing 140 p therebetween is substantially vertically centered withinarea shadowed by the interconnect level feature 101 p. Therefore, theline end spacing 142 p is substantially vertically aligned with the lineend spacing 140 p. This vertical alignment of the line end spacings 142p and 140 p allows for use of a cut mask to define the line end spacings142 p and 140 p. In other words, linear gate level features 116Bp and116Ep are initially defined as a single continuous linear gate levelfeature, and linear gate level features 116Cp and 116Fp are initiallydefined as a single continuous linear gate level feature. Then, a cutmask is used to remove a portion of each of the single continuous lineargate level features so as to form the line end spacings 142 p and 140 p.It should be understood that although the example layout of FIG. 29lends itself to fabrication through use of a cut mask, the layout ofFIG. 29 may also be fabricated without using a cut mask. Additionally,it should be understood that each embodiment disclosed herein as beingsuitable for fabrication through use of a cut mask may also befabricated without using a cut mask.

In one embodiment, the gate contacts 118 p and 120 p are adjustedvertically so as to be edge-aligned with the interconnect level feature101 p. However, such edge alignment between gate contact andinterconnect level feature is not required in all embodiments. Forexample, so long as the gate contacts 118 p and 120 p are placed toenable substantial vertical alignment of the line end spacings 142 p and140 p, the gate contacts 118 p and 120 p may not be edge-aligned withthe interconnect level feature 101 p, although they could be if sodesired. The above-discussed flexibility with regard to gate contactplacement in the direction of extent of the linear gate electrodefeatures is further exemplified in the embodiments of FIGS. 30 and54-60.

FIG. 30 is an illustration showing the cross-coupled transistor layoutof FIG. 29, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 31 is an illustration showing the cross-coupled transistor layoutof FIG. 26, with the rectangular-shaped interconnect level feature 101 preplaced by an S-shaped interconnect level feature 144 p, in accordancewith one embodiment of the present invention. As with the illustratedembodiment of FIG. 26, the S-shaped interconnect level feature 144 p canbe defined as a first interconnect level feature, i.e., as a Metal-1level feature. However, in other embodiments, the S-shaped interconnectlevel feature 144 p may be defined within an interconnect level otherthan the Metal-1 level.

FIG. 32 is an illustration showing the cross-coupled transistor layoutof FIG. 31, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention. It should beappreciated that the S-shaped interconnect level feature 144 p isflipped horizontally relative to the embodiment of FIG. 31 to enableconnection of the inner contacts 120 p and 118 p.

FIG. 33 is an illustration showing the cross-coupled transistor layoutof FIG. 31, with a linear gate level feature 146 p used to make thevertical portion of the connection between the outer contacts 126 p and128 p, in accordance with one embodiment of the present invention. Thus,while the embodiment of FIG. 31 uses vias 132 p and 136 p, and thehigher level interconnect feature 134 p to make the vertical portion ofthe connection between the outer contacts 126 p and 128 p, theembodiment of FIG. 33 uses gate contacts 148 p and 150 p, and the lineargate level feature 146 p to make the vertical portion of the connectionbetween the outer contacts 126 p and 128 p. In the embodiment of FIG.33, the linear gate level feature 146 p serves as a conductor, and isnot used to define a gate electrode of a transistor. It should beunderstood that the linear gate level feature 146 p, used to connect theouter gate contacts 126 p and 128 p, can be placed essentially anywherein the layout, i.e., can be horizontally shifted in either directionaway from the cross-coupled transistors 102 p, 104 p, 106 p, 108 p, asnecessary to satisfy particular layout requirements.

FIG. 34 is an illustration showing the cross-coupled transistor layoutof FIG. 33, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 35 is an illustration showing the cross-coupled transistor layoutof FIG. 33 defined in connection with a multiplexer (MUX), in accordancewith one embodiment of the present invention. In contrast to theembodiment of FIG. 33 which utilizes a non-transistor linear gate levelfeature 146 p to make the vertical portion of the connection between theouter contacts 126 p and 128 p, the embodiment of FIG. 35 utilizes aselect inverter of the MUX to make the vertical portion of theconnection between the outer contacts 126 p and 128 p, wherein theselect inverter of the MUX is defined by transistors 152 p and 154 p.More specifically, transistor 102 p of the cross-coupled transistors isdriven through transistor 152 p of the select inverter. Similarly,transistor 104 p of the cross-coupled transistors is driven throughtransistor 154 p of the select inverter. It should be understood thatthe linear gate level feature 116Gp, used to define the transistors 152p and 154 p of the select inverter and used to connect the outer gatecontacts 126 p and 128 p, can be placed essentially anywhere in thelayout, i.e., can be horizontally shifted in either direction away fromthe cross-coupled transistors 102 p, 104 p, 106 p, 108 p, as necessaryto satisfy particular layout requirements.

FIG. 36 is an illustration showing the cross-coupled transistor layoutof FIG. 35, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 37 is an illustration showing a latch-type cross-coupled transistorlayout, in accordance with one embodiment of the present invention. Thelatch-type cross-coupled transistor layout of FIG. 37 is similar to thatof FIG. 33, with the exception that the gate widths of transistors 102 pand 108 p are reduced relative to the gate widths of transistors 106 pand 104 p. Because transistors 102 p and 108 p perform a signal keepingfunction as opposed to a signal driving function, the gate widths oftransistors 102 p and 108 p can be reduced. As with the embodiment ofFIG. 33, the outer gate contact 126 p is connected to the outer gatecontact 128 p by way of the interconnect level feature 130 p, the gatecontact 148 p, the linear gate level feature 146 p, the gate contact 150p, and the interconnect level feature 138 p.

Also, because of the reduced size of the diffusion regions 110 p and 112p for the keeping transistors 102 p and 108 p, the inner gate contacts120 p and 118 p can be vertically aligned. Vertical alignment of theinner gate contacts 120 p and 118 p may facilitate contact fabrication,e.g., contact lithographic resolution. Also, vertical alignment of theinner gate contacts 120 p and 118 p allows for use of simplelinear-shaped interconnect level feature 156 p to connect the inner gatecontacts 120 p and 118 p. Also, vertical alignment of the inner gatecontacts 120 p and 118 p allows for increased vertical separation of theline end spacings 142 p and 140 p, which may facilitate creation of theline end spacings 142 p and 140 p when formed using separate cut shapesin a cut mask.

FIG. 38 is an illustration showing the cross-coupled transistor layoutof FIG. 37, with the horizontal positions of the inner gate contacts 120p, 118 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 39 is an illustration showing the cross-coupled transistor layoutof FIG. 37, with the interconnect level feature 134 p used to make thevertical portion of the connection between the outer contacts 126 p and128 p, in accordance with one embodiment of the present invention. Thus,while the embodiment of FIG. 37 uses gate contacts 148 p and 150 p, andthe linear gate level feature 146 p to make the vertical portion of theconnection between the outer contacts 126 p and 128 p, the embodiment ofFIG. 39 uses vias 132 p and 136 p, and the interconnect level feature134 p to make the vertical portion of the connection between the outercontacts 126 p and 128 p. In one embodiment of FIG. 39, the interconnectlevel feature 134 p is defined as second interconnect level feature,i.e., Metal-2 level feature. However, in other embodiments, theinterconnect level feature 134 p can be defined within an interconnectlevel other than the second interconnect level. It should be understoodthat the interconnect level feature 134 p, used to connect the outergate contacts 126 p and 128 p, can be placed essentially anywhere in thelayout, i.e., can be horizontally shifted in either direction away fromthe cross-coupled transistors 102 p, 104 p, 106 p, 108 p, as necessaryto satisfy layout requirements.

FIG. 40 is an illustration showing the cross-coupled transistor layoutof FIG. 39, with the horizontal positions of the inner gate contacts 120p, 118 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 41 is an illustration showing the latch-type cross-coupledtransistor layout of FIG. 37, defined in connection with a MUX/latch, inaccordance with one embodiment of the present invention. In contrast tothe embodiment of FIG. 37 which utilizes anon-transistor linear gatelevel feature 146 p to make the vertical portion of the connectionbetween the outer contacts 126 p and 128 p, the embodiment of FIG. 41utilizes a select/clock inverter of the MUX/latch to make the verticalportion of the connection between the outer contacts 126 p and 128 p,wherein the select/clock inverter of the MUX/latch is defined bytransistors 160 p and 162 p. More specifically, transistor 102 p of thecross-coupled transistors is driven through transistor 160 p of theselect/clock inverter. Similarly, transistor 104 p of the cross-coupledtransistors is driven through transistor 162 p of the select/clockinverter. It should be understood that the linear gate level feature 164p, used to define the transistors 160 p and 162 p of the select/clockinverter and used to connect the outer gate contacts 126 p and 128 p,can be placed essentially anywhere in the layout, i.e., can behorizontally shifted in either direction away from the cross-coupledtransistors 102 p, 104 p, 106 p, 108 p, as necessary to satisfyparticular layout requirements.

FIG. 42 is an illustration showing the cross-coupled transistor layoutof FIG. 41, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 43 is an illustration showing the latch-type cross-coupledtransistor layout of FIG. 37, defined to have the outer gate contacts126 p and 128 p connected using a single interconnect level, inaccordance with one embodiment of the present invention. In contrast tothe embodiment of FIG. 37 which utilizes a non-transistor linear gatelevel feature 146 p to make the vertical portion of the connectionbetween the outer contacts 126 p and 128 p, the embodiment of FIG. 43uses a single interconnect level to make the horizontal and verticalportions of the connection between the outer contacts 126 p and 128 p.The gate electrode of transistor 102 p is connected to the gateelectrode of transistor 104 p through gate contact 126 p, throughhorizontal interconnect level feature 166 p, through verticalinterconnect level feature 168 p, through horizontal interconnect levelfeature 170 p, and through gate contact 128 p. In one embodiment, theinterconnect level features 166 p, 168 p, and 170 p are firstinterconnect level features (Metal-1 features). However, in otherembodiments, the interconnect level features 166 p, 168 p, and 170 p canbe defined collectively within any other interconnect level.

FIG. 44 is an illustration showing the cross-coupled transistor layoutof FIG. 43, with the horizontal positions of the inner gate contacts 118p, 120 p and outer gate contacts 126 p, 128 p respectively reversed, inaccordance with one embodiment of the present invention.

FIG. 45 is an illustration showing a cross-coupled transistor layout inwhich all four gate contacts 126 p, 128 p, 118 p, and 120 p of thecross-coupled coupled transistors are placed therebetween, in accordancewith one embodiment of the present invention. Specifically, the gatecontacts 126 p, 128 p, 118 p, and 120 p of the cross-coupled coupledtransistors are placed vertically between the diffusion regions 110 pand 112 p that define the cross-coupled coupled transistors. The gateelectrode of transistor 102 p is connected to the gate electrode oftransistor 104 p through gate contact 126 p, through horizontalinterconnect level feature 172 p, through vertical interconnect levelfeature 174 p, through horizontal interconnect level feature 176 p, andthrough gate contact 128 p. In one embodiment, the interconnect levelfeatures 172 p, 174 p, and 176 p are first interconnect level features(Metal-1 features). However, in other embodiments, the interconnectlevel features 172 p, 174 p, and 176 p can be defined collectivelywithin any other interconnect level. The gate electrode of transistor108 p is connected to the gate electrode of transistor 106 p throughgate contact 120 p, through S-shaped interconnect level feature 144 p,and through gate contact 118 p. The S-shaped interconnect level feature144 p can be defined within any interconnect level. In one embodiment,the S-shaped interconnect level feature is defined within the firstinterconnect level (Metal-1 level).

FIG. 46 is an illustration showing the cross-coupled transistor layoutof FIG. 45, with multiple interconnect levels used to connect the gatecontacts 126 p and 128 p, in accordance with one embodiment of thepresent invention. The gate electrode of transistor 102 p is connectedto the gate electrode of transistor 104 p through gate contact 126 p,through horizontal interconnect level feature 172 p, through via 180 p,through vertical interconnect level feature 178 p, through via 182 p,through horizontal interconnect level feature 176 p, and through gatecontact 128 p. In one embodiment, the horizontal interconnect levelfeatures 172 p and 176 p are defined within the same interconnect level,e.g., Metal-1 level, and the vertical interconnect level feature 178 pis defined within a higher interconnect level, e.g., Metal-2 level. Itshould be understood, however, that in other embodiments each ofinterconnect level features 172 p, 178 p, and 176 p can be defined inseparate interconnect levels.

FIG. 47 is an illustration showing the cross-coupled transistor layoutof FIG. 45, with increased vertical separation between line end spacings184 p and 186 p, in accordance with one embodiment of the presentinvention. The increased vertical separation between line end spacings184 p and 186 p can facilitate creation of the line end spacings 184 pand 186 p when formed using separate cut shapes in a cut mask.

FIG. 48 is an illustration showing the cross-coupled transistor layoutof FIG. 45, using an L-shaped interconnect level feature 188 p toconnect the gate contacts 120 p and 118 p, in accordance with oneembodiment of the present invention.

FIG. 49 is an illustration showing the cross-coupled transistor layoutof FIG. 48, with the horizontal position of gate contacts 126 p and 118p reversed, and with the horizontal position of gate contacts 120 p and128 p reversed, in accordance with one embodiment of the presentinvention.

FIG. 50 is an illustration showing the cross-coupled transistor layoutof FIG. 48, with increased vertical separation between line end spacings184 p and 186 p, in accordance with one embodiment of the presentinvention. The increased vertical separation between line end spacings184 p and 186 p can facilitate creation of the line end spacings 184 pand 186 p when formed using separate cut shapes in a cut mask.

FIG. 51 is an illustration showing the cross-coupled transistor layoutof FIG. 45, in which gate contacts 120 p and 118 p are verticallyaligned, in accordance with one embodiment of the present invention. Alinear-shaped interconnect level feature 190 p is used to connect thevertically aligned gate contacts 120 p and 118 p. Also, in theembodiment of FIG. 51, an increased vertical separation between line endspacings 184 p and 186 p is provided to facilitate creation of the lineend spacings 184 p and 186 p when formed using separate cut shapes in acut mask, although use of a cut mask to fabricate the layout of FIG. 51is not specifically required.

FIG. 52 is an illustration showing the cross-coupled transistor layoutof FIG. 45, in which a linear-shaped interconnect level feature 192 p isused to connect the non-vertically-aligned gate contacts 120 p and 118p, in accordance with one embodiment of the present invention. It shouldbe appreciated that the linear-shaped interconnect level feature 192 pis stretched vertically to cover both of the gate contacts 120 p and 118p.

FIG. 53 is an illustration showing the cross-coupled transistor layoutof FIG. 52, with multiple interconnect levels used to connect the gatecontacts 126 p and 128 p, in accordance with one embodiment of thepresent invention. The gate electrode of transistor 102 p is connectedto the gate electrode of transistor 104 p through gate contact 126 p,through horizontal interconnect level feature 172 p, through via 180 p,through vertical interconnect level feature 178 p, through via 182 p,through horizontal interconnect level feature 176 p, and through gatecontact 128 p. In one embodiment, the horizontal interconnect levelfeatures 172 p and 176 p are defined within the same interconnect level,e.g., Metal-1 level, and the vertical interconnect level feature 178 pis defined within a higher interconnect level, e.g., Metal-2 level. Itshould be understood, however, that in other embodiments each ofinterconnect level features 172 p, 178 p, and 176 p can be defined inseparate interconnect levels.

FIG. 54 is an illustration showing the cross-coupled transistor layoutof FIG. 53, with the vertical positions of gate contacts 118 p and 120 padjusted to enable alignment of the line end spacings betweenco-linearly aligned gate level features, in accordance with oneembodiment of the present invention. Specifically, gate contact 118 p isadjusted vertically upward, and gate contact 120 p is adjustedvertically downward. The linear gate level features 116Bp and 116Ep arethen adjusted such that the line end spacing 184 p therebetween issubstantially vertically centered within area shadowed by theinterconnect level feature 192 p. Similarly, the linear gate levelfeatures 116Cp and 116Fp are then adjusted such that the line endspacing 186 p therebetween is substantially vertically centered withinarea shadowed by the interconnect level feature 192 p. Therefore, theline end spacing 184 p is substantially vertically aligned with the lineend spacing 186 p. This vertical alignment of the line end spacings 184p and 186 p allows for use of a cut mask to define the line end spacings184 p and 186 p. In other words, linear gate level features 116Bp and116Ep are initially defined as a single continuous linear gate levelfeature, and linear gate level features 116Cp and 116Fp are initiallydefined as a single continuous linear gate level feature. Then, a cutmask is used to remove a portion of each of the single continuous lineargate level features so as to form the line end spacings 184 p and 186 p.As previously discussed with regard to FIG. 29, although edge-alignmentbetween the gate contacts 118 p, 120 p and the interconnect levelfeature 192 p can be utilized in one embodiment, it should be understoodthat such edge-alignment between gate contact and interconnect levelfeature is not required in all embodiments.

FIG. 55 is an illustration showing a cross-coupled transistor layout inwhich the four gate contacts 126 p, 128 p, 120 p, and 118 p are placedwithin three consecutive horizontal tracks of an interconnect level, inaccordance with one embodiment of the present invention. The gateelectrode of transistor 102 p is connected to the gate electrode oftransistor 104 p through gate contact 126 p, through horizontalinterconnect level feature 402 p, through gate contact 418 p, throughvertical gate level feature 404 p, through gate contact 416 p, throughhorizontal interconnect level feature 424 p, and through gate contact128 p. The vertical gate level feature 404 p represents a common node towhich the gate electrodes of transistors 426 p and 428 p are connected.It should be understood that the vertical gate level feature 404 p canbe shifted left or right relative to the cross-coupled transistors 102p, 104 p, 106 p, 108 p, as necessary for layout purposes. Also, the gateelectrode of transistor 106 p is connected to the gate electrode oftransistor 108 p through gate contact 118 p, through horizontalinterconnect level feature 190 p, and through gate contact 120 p.

It should be appreciated that placement of gate contacts 126 p, 128 p,120 p, and 118 p within three consecutive horizontal interconnect leveltracks allows for an interconnect level track 414 p to pass through thecross-coupled transistor layout. Also, it should be understood that theinterconnect level features 402 p, 424 p, and 190 p can be defined inthe same interconnect level or in different interconnect levels. In oneembodiment, each of the interconnect level features 402 p, 424 p, and190 p is defined in a first interconnect level (Metal-1 level).

FIG. 56 is an illustration showing the cross-coupled transistor layoutof FIG. 55, in which a non-transistor gate level feature 430 p is usedto make the vertical portion of the connection between gate contacts 126p and 126 p, in accordance with one embodiment of the present invention.The gate electrode of transistor 102 p is connected to the gateelectrode of transistor 104 p through gate contact 126 p, throughhorizontal interconnected level feature 402 p, through gate contact 418p, through vertical non-transistor gate level feature 430 p, throughgate contact 416 p, through horizontal interconnect level feature 424 p,and through gate contact 128 p.

FIG. 57 is an illustration showing a cross-coupled transistor layout inwhich the four gate contacts 126 p, 128 p, 120 p, and 118 p are placedwithin three consecutive horizontal tracks of an interconnect level, andin which multiple interconnect levels are used to connect the gatecontacts 126 p and 128 p, in accordance with one embodiment of thepresent invention. The gate electrode of transistor 102 p is connectedto the gate electrode of transistor 104 p through gate contact 126 p,through horizontal interconnect level feature 432 p, through via 434 p,through vertical interconnect level feature 436 p, through via 438 p,through horizontal interconnect level feature 440 p, and through gatecontact 128 p. The vertical interconnect level feature 436 p is definedwithin an interconnect level different from the interconnect level inwhich the horizontal interconnect level features 432 p and 440 p aredefined. In one embodiment, the horizontal interconnect level features432 p and 440 p are defined within a first interconnect level (Metal-1level), and the vertical interconnect level feature 436 p is definedwithin a second interconnect level (Metal-2 level). It should beunderstood that the vertical interconnect level feature 436 p can beshifted left or right relative to the cross-coupled transistors 102 p,104 p, 106 p, 108 p, as necessary for layout purposes. Also, the gateelectrode of transistor 106 p is connected to the gate electrode oftransistor 108 p through gate contact 118 p, through horizontalinterconnect level feature 190 p, and through gate contact 120 p.

FIG. 58 is an illustration showing the cross-coupled transistor layoutof FIG. 57, in which the gate contacts 126Ap, 118Ap, 120Ap, and 128Apare extended in the vertical direction to provided additional overlapwith their respective underlying gate level feature, in accordance withone embodiment of the present invention. The additional overlap of thegate level features by the gate contacts 126Ap, 118Ap, 120Ap, and 128Apmay be provided to satisfy design rules.

FIG. 59 is an illustration showing the cross-coupled transistor layoutof FIG. 57, in which the gate contacts 126 p, 118 p, 120 p, and 128 pare placed within four consecutive interconnect level tracks with anintervening vacant interconnect level track 704 p, in accordance withone embodiment of the present invention. The gate electrode oftransistor 102 p is connected to the gate electrode of transistor 104 pthrough gate contact 126 p, through horizontal interconnect levelfeature 432 p, through via 434 p, through vertical interconnect levelfeature 436 p, through via 438 p, through horizontal interconnect levelfeature 440 p, and through gate contact 128 p. The gate electrode oftransistor 106 p is connected to the gate electrode of transistor 108 pthrough gate contact 118 p, through L-shaped interconnect level feature450 p, and through gate contact 120 p. As shown at locations 706 p and708 p, the L-shaped interconnect level feature 450 p can be extendedbeyond the gate contacts 120 p and 118 p to provide sufficient overlapof the gate contacts by the L-shaped interconnect level feature 450 p,as needed to satisfy design rules.

FIG. 60 is an illustration showing the cross-coupled transistor layoutof FIG. 59, with a variation in the overlap of the gate contact 120 p bythe L-shaped interconnect level feature 450 p, in accordance with oneembodiment of the present invention. The overlap region 709 p is turnedhorizontally so as to align with the horizontal interconnect levelfeature 440 p.

FIGS. 61-94 are illustrations showing variants of the cross-coupledtransistor layouts of FIGS. 26 and 28-60, respectively. As previouslymentioned, essentially any cross-coupled transistor layout defined inaccordance with a linear gate level can be represented in an alternatemanner by horizontally and/or vertically reversing placement of the gatecontacts that are used to connect one or both pairs of the fourtransistors of the cross-coupled transistor configuration. Also,essentially any cross-coupled transistor layout defined in accordancewith a linear gate level can be represented in an alternate manner bymaintaining gate contact placements and by modifying each routing pathused to connect one or both pairs of the four transistors of thecross-coupled transistor configuration.

FIGS. 95-99 show exemplary cross-coupled transistor layouts defined inaccordance with the linear gate level, in which a folded transistorlayout technique is implemented. A folded transistor is defined as aplurality of transistors whose gate electrodes share an identicalelectrical connectivity configuration. In other words, each individualtransistor of a given folded transistor has its gate electrode connectedto a common node and is defined to electrically interface with a commondiffusion region. It should be understood that although each individualtransistor of a given folded transistor has its gate electrode connectedto a common diffusion region, it is not required that the commondiffusion region be continuous, i.e., monolithic. For example, diffusionregions that are of the same type but are physically separated from eachother, and have an electrical connection to a common output node, andshare a common source/drain, satisfy the common diffusion regioncharacteristic of the folded transistor.

In the example layout of FIG. 95, a first pair of the cross-coupledtransistors is defined by a folded transistor 6901Ap/6901Bp and by atransistor 6903 p. Each of the individual transistors 6901Ap and 6901Bpthat form the folded transistor is connected to a common diffusionregion 6905 p and has its gate electrode connected to a common node 6907p through respective gate contacts 6909Ap and 6909Bp. The gate contacts6909Ap and 6909Bp are connected to a gate contact 6921 p of transistor6903 p by way of a metal 1 interconnect level feature 6911 p, a contact6913 p, a gate level feature 6915 p, a contact 6917 p, and a metal 1interconnect level feature 6919 p. A second pair of the cross-coupledtransistors is defined by a folded transistor 6923Ap/6923Bp and by atransistor 6925 p. Each of the individual transistors 6923Ap and 6923Bpthat form the folded transistor is connected to a common diffusionregion 6927 p and has its gate electrode connected to a common node 6929p through respective gate contacts 6931Ap and 6931Bp. The gate contacts6931Ap and 6931Bp are connected to a gate contact 6933 p of transistor6925 p by way of a metal 1 interconnect level feature 6935 p.Transistors 6901Ap, 6901Bp, and 6925 p are electrically interfaced withthe diffusion region 6905 p. Also, transistors 6923Ap, 6923Bp, and 6903p are electrically interfaced with the diffusion region 6927 p.Additionally, although not explicitly shown, diffusion regions 6905 pand 6927 p are connected to a common output node.

FIG. 96 shows a variant of the cross-coupled transistor layout of FIG.95, in which the connection between the folded transistor 6901Ap/6901Bpand the transistor 6903 p is made using an alternate conductive paththrough the chip. Specifically, the gate contacts 6909Ap and 6909Bp areconnected to the gate contact 6921 p of transistor 6903 p by way of ametal 1 interconnect level feature 7001 p, a via 7003 p, a metal 2interconnect level feature 7005 p, a via 7007 p, and a metal 1interconnect level feature 7009 p.

In the example layout of FIG. 97, a first pair of the cross-coupledtransistors is defined by a folded transistor 7101Ap/7101Bp and by afolded transistor 7103Ap/7103Bp. Gate contacts 7105Ap and 7105Bp areconnected to gate contacts 7107Ap and 7107Bp by way of a metal 1interconnect level feature 7109 p, a via 7111 p, a metal 2 interconnectlevel feature 7113 p, a via 7115 p, and a metal 1 interconnect levelfeature 7117 p. A second pair of the cross-coupled transistors isdefined by a folded transistor 7119Ap/7119Bp and by a folded transistor7121Ap/7121Bp. Gate contacts 7123Ap and 7123Bp are connected to gatecontacts 7125Ap and 7125Bp by way of a metal 1 interconnect levelfeature 7127 p, a via 7129 p, a metal 2 interconnect level feature 7131p, a via 7133 p, a metal 1 interconnect level feature 7135 p, a via 7137p, a metal 2 interconnect level feature 7139 p, a via 7141 p, and ametal 1 interconnect level feature 7143 p. Transistors 7101Ap, 7101Bp,7121Ap, and 7121Bp are electrically interfaced with diffusion region7145 p. Also, transistors 7119Ap, 7119Bp, 7103Ap, and 7103Bp areelectrically interfaced with diffusion region 7147 p. Additionally,although not explicitly shown, portions of diffusion regions 7145 p and7147 p which are electrically interfaced with the transistors 7101Ap,7101Bp, 7103Ap, 7103Bp, 7119Ap, 7119Bp, 7121Ap, and 7121Bp are connectedto a common output node.

FIG. 98 shows a variant of the cross-coupled transistor layout of FIG.97, in which the electrical connections between the cross-coupledtransistors are made using an alternate conductive paths through thechip. Specifically, the gate contacts 7105Ap and 7105Bp are connected tothe gate contacts 7107Ap and 7107Bp by way of a metal 1 interconnectlevel feature 7201 p, a contact 7203 p, a gate level feature 7205 p, acontact 7207 p, and a metal 1 interconnect level feature 7209 p. Also,the gate contacts 7123Ap and 7123Bp are connected to the gate contacts7125Ap and 7125Bp by way of a metal 1 interconnect level feature 7211 p.In this embodiment, the metal 1 interconnect level in unrestricted withregard to bends in conductive features. Therefore, the metal 1interconnect level feature 7211 p can be defined to “snake” through themetal 1 interconnect level to make the required cross-coupled transistorconnections, as permitted by surrounding layout features.

FIG. 99 shows a variant of the cross-coupled transistor layout of FIG.97, in which the connection between the folded transistor 7101Ap/7101Bpand the folded transistor 7103Ap/7103Bp is made using an alternateconductive path through the chip. Specifically, the gate contacts 7105Apand 7105Bp are connected to the gate contacts 7107Ap and 7107Bp by wayof the metal 1 interconnect level feature 7201 p, the contact 7203 p,the gate level feature 7205 p, the contact 7207 p, and the metal 1interconnect level feature 7209 p. It should be understood that thecross-coupled transistor layouts utilizing folded transistors as shownin FIGS. 95-99 are provided by way of example, and should not beconstrued as fully inclusive.

In each FIGS. 26-99, the cross-coupled transistor connections have beendescribed by tracing through the various conductive features of eachconductive path used to connect each pair of transistors in thecross-coupled layout. It should be appreciated that the conductive pathused to connect each pair of transistors in a given cross-coupled layoutcan traverse through conductive features any number of levels of thechip, utilizing any number of contacts and vias as necessary. For easeof description with regard to FIGS. 100 through 192, the conductivepaths used to connect the various NMOS/PMOS transistor pairs in eachcross-coupled transistor layout are identified by heavy black linesdrawn over the corresponding layout features.

As previously mentioned, FIGS. 26-99 do not explicitly show connectionof the diffusion regions of the cross-coupled transistors to a commonnode, although this connection is present. FIGS. 100-111 show exemplarycross-coupled transistor layouts in which the n-type and p-typediffusion regions of the cross-coupled transistors are shown to beelectrically connected to a common node. The conductive path used toconnect the diffusion regions of the cross-coupled transistors to thecommon node in each of FIGS. 100-111 is identified by a heavy blackdashed line drawn over the corresponding layout features. For ease ofdescription, FIGS. 112-148 do not show the heavy black dashed linecorresponding to the conductive path used to connect the diffusionregions of the cross-coupled transistors to the common node. However,some of FIGS. 112-148 do show the layout features associated with theconductive path, or a portion thereof, used to connect the diffusionregions of the cross-coupled transistors to the common node. Again,although not explicitly shown in each of FIGS. 26-148, it should beunderstood that each of the exemplary cross-coupled transistor layoutincludes a conductive path that connects the diffusion regions of thecross-coupled transistors to a common output node.

FIGS. 112-148 show a number of exemplary cross-coupled transistorlayouts in which the p-type diffusion regions that are electricallyinterfaced with the cross-coupled transistors are physically separatedfrom each other. For example, with regard to FIG. 112, the p-typediffusion region 8601 p is physically separated from the p-typediffusion region 8603 p. However, the p-type diffusion regions 8601 pand 8603 p are electrically connected to each other by way of contact8605 p, metal 1 interconnect level feature 8607 p, and contact 8609 p.Although not shown, the diffusion regions 8601 p and 8603 p are alsoelectrically connected to diffusion region 8611 p. It should beunderstood that a variant of each cross-coupled transistor layout asshown in each of FIGS. 112-148, can be defined by changing the p-typediffusion regions as shown to n-type diffusion regions, and by alsochanging the n-type diffusion regions as shown to p-type diffusionsregions. Therefore, such variants of FIGS. 112-148 illustrate a numberof exemplary cross-coupled transistor layouts in which the n-typediffusion regions that are electrically interfaced with thecross-coupled transistors are physically separated from each other.

FIGS. 149-175 show a number of exemplary cross-coupled transistorlayouts defined using two gate contacts to connect one pair ofcomplementary (i.e., NMOS/PMOS) transistors in the cross-coupledtransistor layout to each other, and using no gate contact to connectthe other pair of complementary transistors in the cross-coupledtransistor layout to each other. It should be understood that two gateelectrodes of each pair of cross-coupled transistors, when considered asa single node, are electrically connected through at least one gatecontact to circuitry external to the cross-coupled transistor portion ofthe layout. Therefore, it should be understood that the gate electrodesmentioned above, or absence thereof, with regard to connecting each pairof complementary transistors in the cross-coupled transistor layout,refer to gate electrodes defined within the cross-coupled transistorportion of the layout.

For example, FIG. 149 shows a cross-coupled transistor layout in which agate electrode of transistor 12301 p is electrically connected to a gateelectrode of transistor 12303 p by way of two gate contacts 12309 p and12311 p in combination with other conductive features. Also, the gateelectrodes of transistors 12305 p and 12307 p are defined as a single,continuous linear conductive feature within the gate level. Therefore, agate contact is not required to electrically connect the gate electrodesof transistors 12305 p and 12307 p. The conductive path used to connectthe diffusion regions of the cross-coupled transistors to the commonoutput node in each of FIGS. 149-175 is identified by a heavy blackdashed line drawn over the corresponding layout features.

It should be appreciated that the cross-coupled transistor layoutdefined using two gate contacts to connect one pair of complementarytransistors and no gate contact to connect the other pair ofcomplementary transistors can be implemented in as few as two gateelectrode tracks, wherein a gate electrode track is defined as a virtualline extending across the gate level in a parallel relationship to itsneighboring gate electrode tracks. These two gate electrode tracks canbe located essentially anywhere in the layout with regard to each other.In other words, these two gate electrode tracks are not required to belocated adjacent to each other, although such an arrangement ispermitted, and in some embodiments may be desirable. The cross-coupledtransistor layout embodiments of FIGS. 149-175 can be characterized inthat two gate electrodes of one pair of connected complementarytransistors in the cross-coupled layout are defined from a single,continuous linear conductive feature defined in the gate level.

FIGS. 176-191 show a number of exemplary cross-coupled transistorlayouts defined using no gate contacts to connect each pair ofcomplementary transistors in the cross-coupled transistor layout. Again,it should be understood that two gate electrodes of each pair ofcross-coupled transistors, when considered as a single node, areelectrically connected through at least one gate contact to circuitryexternal to the cross-coupled transistor portion of the layout.Therefore, it should be understood that the absence of gate electrodeswith regard to connecting each pair of complementary transistors in thecross-coupled transistor layout refers to an absence of gate electrodesdefined within the cross-coupled transistor portion of the layout.

For example, FIG. 176 shows a cross-coupled transistor layout in whichgate electrodes of transistors 15001 p and 15003 p are defined as asingle, continuous linear conductive feature within the gate level.Therefore, a gate contact is not required to electrically connect thegate electrodes of transistors 15001 p and 15003 p. Also, gateelectrodes of transistors 15005 p and 15007 p are defined as a single,continuous linear conductive feature within the gate level. Therefore, agate contact is not required to electrically connect the gate electrodesof transistors 15005 p and 15007 p. The conductive path used to connectthe diffusion regions of the cross-coupled transistors to the commonoutput node in each of FIGS. 176-191 is identified by a heavy blackdashed line drawn over the corresponding layout features. It should beappreciated that the cross-coupled transistor layout defined using nogate contact to connect each pair of complementary transistors can beimplemented in as few as one gate electrode track. The cross-coupledtransistor layout embodiments of FIGS. 176-191 can be characterized inthat each pair of connected complementary transistors in thecross-coupled layout has its gate electrodes defined from a single,continuous linear conductive feature defined in the gate level.

FIG. 192 shows another exemplary cross-couple transistor layout in whichthe common diffusion node shared between the cross-coupled transistors16601 p, 16603 p, 16605 p, and 16607 p has one or more transistorsdefined thereover. Specifically, FIG. 192 shows that transistors 16609Apand 16609Bp are defined over the diffusion region 16613 p betweentransistors 16605 p and 16603 p. Also, FIG. 192 shows that transistors16611Ap and 16611Bp are defined over the diffusion region 16615 pbetween transistors 16601 p and 16607 p. It should be understood thatdiffusion regions 16613 p and 16615 p define the common diffusion nodeto which each of the cross-coupled transistors 16601 p, 16603 p, 16605p, and 16607 p is electrically interfaced. It should be appreciated thatwith this type of cross-coupled transistor layout, driver transistors,such as transistors 16609Ap, 16609Bp, 16611Ap, and 16611Bp, can bedisposed over the common diffusion node of the cross-coupledtransistors. Hence, the cross-coupled transistors can be considered asbeing placed “outside” of the driver transistors.

As illustrated in FIGS. 26-192, the cross-coupled transistor layoutusing a linear gate level can be defined in a number of different ways.A number of observations associated with the cross-coupled transistorlayout defined using the linear gate level are as follows:

-   -   In one embodiment, an interconnect level parallel to the gate        level is used to connect the two “outside” transistors, i.e., to        connect the two outer gate contacts.    -   In one embodiment, the end gaps, i.e., line end spacings,        between co-aligned gate electrode features in the area between        the n and p diffusion regions can be substantially vertically        aligned to enable line end cutting.    -   In one embodiment, the end gaps, i.e., line end spacings,        between gate electrode features in the area between the n and p        diffusion regions can be separated as much as possible to allow        for separation of cut shapes, or to prevent alignment of gate        electrode feature line ends.    -   In one embodiment, the interconnect levels can be configured so        that contacts can be placed on a grid to enhance contact        printing.    -   In one embodiment, the contacts can be placed so that a minimal        number of first interconnect level (Metal-1 level) tracks are        occupied by the cross-couple connection.    -   In one embodiment, the contacts can be placed to maximize the        available diffusion area for device size, e.g., transistor        width.    -   In one embodiment, the contacts can be shifted toward the edges        of the interconnect level features to which they connect to        allow for better alignment of gate electrode feature line ends.    -   In pertinent embodiments, it should be noted that the vertical        connection between the outside transistors of the cross-coupled        transistor layout can be shifted left or right depending on the        specific layout requirements.    -   There is no distance requirement between the n and p diffusion        regions. If there are more interconnect level tracks available        between the n and p diffusion region, the available interconnect        level tracks can be allocated as necessary/appropriate for the        layout.    -   The four transistors of the cross-coupled transistor        configuration, as defined in accordance with the linear gate        level, can be separated from each other within the layout by        arbitrary distances in various embodiments.    -   In one embodiment, the linear gate electrode features are placed        according to a virtual grid or virtual grate. However, it should        be understood that in other embodiments the linear gate        electrode features, although oriented to have a common direction        of extent, are placed without regard to a virtual grid or        virtual grate.    -   Each linear gate electrode feature is allowed to have one or        more contact head portion(s) along its line of extent, so long        as the linear gate electrode feature does not connect directly        within the gate level to another linear gate electrode feature        having a different, yet parallel, line of extent.    -   Diffusion regions associated with the cross-coupled transistor        configuration, as defined in accordance with the linear gate        level, are not restricted in size or shape.    -   The four transistors of the cross-coupled transistor        configuration, as defined in accordance with the linear gate        level, may vary in size as required to satisfy electrical        requirements.    -   Essentially any cross-coupled transistor configuration layout        defined in accordance with a linear gate level can be        represented in an alternate manner by horizontally and/or        vertically reversing placement of the gate contacts that are        used to connect one or both pairs of the four transistors of the        cross-coupled transistor configuration.    -   Essentially any cross-coupled transistor configuration layout        defined in accordance with a linear gate level can be        represented in an alternate manner by maintaining gate contact        placements and by modifying each routing path used to connect        one or both pairs of the four transistors of the cross-coupled        transistor configuration.    -   A cross-coupled transistor configuration layout defined in        accordance with a linear gate level can be optimized for a        fabrication process that utilizes a cut mask.    -   In various embodiments, connections between gates of        cross-coupled transistors can be made in essentially any manner        by utilizing any level within the chip, any number of levels in        the chip, any number of contacts, and/or any number of vias.

It should be appreciated that in the embodiments of FIGS. 26-192, anumber of features and connections are not shown in order to avoidunnecessarily obscuring the cross-couple transistors in the variouslayouts. For example, in the embodiments of FIGS. 26-60, connections tosource and drains are not shown. Also, it should be understood that inthe exemplary embodiments of FIGS. 26-192, some features and connectionsthat are not directly associated with the four cross-coupled transistorsare displayed for exemplary purposes and are not intended to representany restriction on the correspondingly displayed cross-coupledtransistor layout.

Based on the foregoing, a cross-coupled transistor layout using commonlyoriented linear gate level features and transistors having physicallyseparate gate electrodes can be defined according to either of thefollowing embodiments, among others:

-   -   all four gate contacts used to connect each pair of        complementary transistors in the cross-coupled transistor layout        are placed between the diffusion regions associated with the        cross-coupled transistor layout,    -   two gate contacts used to connect one pair of complementary        transistors placed between the diffusion regions associated with        the cross-coupled transistor layout, and two gate contacts used        to connect another pair of complementary transistors placed        outside the diffusion regions with one of these two gate        contacts placed outside of each diffusion region,    -   all four gate contacts used to connect each pair of        complementary transistors placed outside the diffusion regions        associated with the cross-coupled transistor layout,    -   three gate contacts placed outside the diffusion regions        associated with the cross-coupled transistor layout, and one        gate contact placed between the diffusion regions associated        with the cross-coupled transistor layout, and    -   three gate contacts placed between the diffusion regions        associated with the cross-coupled transistor layout, and one        gate contact placed outside one of the diffusion regions        associated with the cross-coupled transistor layout.

It should be understood that the cross-coupled transistor layoutsimplemented within the restricted gate level layout architecture asdisclosed herein can be stored in a tangible form, such as in a digitalformat on a computer readable medium. Also, the invention describedherein can be embodied as computer readable code on a computer readablemedium. The computer readable medium is any data storage device that canstore data which can thereafter be read by a computer system. Examplesof the computer readable medium include hard drives, network attachedstorage (NAS), read-only memory, random-access memory, CD-ROMs, CD-Rs,CD-RWs, magnetic tapes, and other optical and non-optical data storagedevices. The computer readable medium can also be distributed over anetwork of coupled computer systems so that the computer readable codeis stored and executed in a distributed fashion.

Any of the operations described herein that form part of the inventionare useful machine operations. The invention also relates to a device oran apparatus for performing these operations. The apparatus may bespecially constructed for the required purpose, such as a specialpurpose computer. When defined as a special purpose computer, thecomputer can also perform other processing, program execution orroutines that are not part of the special purpose, while still beingcapable of operating for the special purpose. Alternatively, theoperations may be processed by a general purpose computer selectivelyactivated or configured by one or more computer programs stored in thecomputer memory, cache, or obtained over a network. When data isobtained over a network the data maybe processed by other computers onthe network, e.g., a cloud of computing resources.

The embodiments of the present invention can also be defined as amachine that transforms data from one state to another state. The datamay represent an article, that can be represented as an electronicsignal and electronically manipulate data. The transformed data can, insome cases, be visually depicted on a display, representing the physicalobject that results from the transformation of data. The transformeddata can be saved to storage generally, or in particular formats thatenable the construction or depiction of a physical and tangible object.In some embodiments, the manipulation can be performed by a processor.In such an example, the processor thus transforms the data from onething to another. Still further, the methods can be processed by one ormore machines or processors that can be connected over a network. Eachmachine can transform data from one state or thing to another, and canalso process data, save data to storage, transmit data over a network,display the result, or communicate the result to another machine.

While this invention has been described in terms of several embodiments,it will be appreciated that those skilled in the art upon reading thepreceding specifications and studying the drawings will realize variousalterations, additions, permutations and equivalents thereof. Therefore,it is intended that the present invention includes all such alterations,additions, permutations, and equivalents as fall within the true spiritand scope of the invention.

What is claimed is:
 1. An integrated circuit, comprising: a gateelectrode level region having a number of adjacently positioned gatelevel feature layout channels, each gate level feature layout channelextending lengthwise in a first direction and widthwise in a seconddirection perpendicular to the first direction, wherein each of thenumber of adjacently positioned gate level feature layout channelsincludes at least one gate level feature, each gate level feature havinga first end located adjacent to a line end spacing and a second endlocated adjacent to another line end spacing, each gate level featureforming an electrically conductive path extending between its first andsecond ends, wherein the gate electrode level region includes a firstgate level feature that includes a first part that forms a gateelectrode of a first transistor of a first transistor type and a secondpart that forms a gate electrode of a first transistor of a secondtransistor type, wherein the gate electrode of the first transistor ofthe first transistor type is substantially co-aligned with the gateelectrode of the first transistor of the second transistor type along afirst common line of extent in the first direction, and wherein the gateelectrode of the first transistor of the first transistor type iselectrically connected to the gate electrode of the first transistor ofthe second transistor type through the first gate level feature, whereinthe gate electrode level region includes a second gate level featurethat forms a gate electrode of a second transistor of the firsttransistor type, wherein the gate electrode level region includes athird gate level feature that forms a gate electrode of a secondtransistor of the second transistor type, wherein the second and thirdgate level features are located in different gate level feature layoutchannels, wherein gate electrode of the second transistor of the firsttransistor type is electrically connected to the gate electrode of thesecond transistor of the second transistor type, wherein the first andsecond transistors of the first transistor type are collectivelyseparated from the first and second transistors of the second transistortype by an inner portion of the gate electrode level region, whereineach of the first and second transistors of the first transistor type isformed in part by a shared diffusion region of a first diffusion typelocated on a first side of the first gate level feature, wherein each ofthe first and second transistors of the second transistor type is formedin part by a shared diffusion region of a second diffusion type locatedon a second side of the first gate level feature, and wherein the firstand second sides of the first gate level feature are opposite sides ofthe first gate level feature.
 2. An integrated circuit as recited inclaim 1, wherein the gate electrode level region includes anon-transistor gate level feature that does not form a gate electrode ofa transistor and that is positioned between at least two other gatelevel features in the second direction.
 3. An integrated circuit asrecited in claim 2, wherein a size of the non-transistor gate levelfeature as measured in the second direction is substantially equal to asize of at least one of the at least two other gate level featuresbetween which the non-transistor gate level feature is positioned.
 4. Anintegrated circuit as recited in claim 1, wherein each gate levelfeature has a substantially linear shape within the gate electrode levelregion.
 5. An integrated circuit as recited in claim 4, wherein the gateelectrode level region includes a non-transistor gate level feature thatdoes not form a gate electrode of a transistor and that is positionedbetween at least two other gate level features in the second direction.6. An integrated circuit as recited in claim 5, wherein thenon-transistor gate level feature has a length as measured in the firstdirection substantially equal to a length of a gate level feature thatforms gate electrodes of both a transistor of the first transistor typeand a transistor of the second transistor type.
 7. An integrated circuitas recited in claim 1, wherein the second gate level feature iselectrically connected to the third gate level feature through a firstelectrical connection that extends in part through a single interconnectlevel formed above the gate electrode level region.
 8. An integratedcircuit as recited in claim 7, wherein the gate electrodes of the firstand second transistors of the first transistor type are positionedaccording to a gate pitch defined as an equal center-to-center spacingmeasured in the second direction between adjacent gate electrodes, andwherein the gate electrodes of the first and second transistors of thesecond transistor type are positioned according to the gate pitch.
 9. Anintegrated circuit as recited in claim 8, wherein all gate electrodeswithin the gate electrode level region are positioned according to thegate pitch such that a distance measured in the second direction betweenfirst-direction-oriented centerlines of any two gate electrodes withinthe gate electrode level region is substantially equal to an integermultiple of the gate pitch.
 10. An integrated circuit as recited inclaim 9, wherein the shared diffusion region of the first diffusion typeis electrically connected to the shared diffusion region of the seconddiffusion type through a second electrical connection that extends inpart through a single interconnect level formed above the gate electrodelevel region.
 11. An integrated circuit as recited in claim 10, whereinthe shared diffusion region of the first diffusion type is electricallyconnected to the shared diffusion region of the second diffusion typethrough a second electrical connection that extends through at least twointerconnect levels formed above the gate electrode level region.
 12. Anintegrated circuit as recited in claim 9, further comprising: a firstgate contact defined to physically contact the first gate level feature;a second gate contact defined to physically contact the second gatelevel feature; and a third gate contact defined to physically contactthe third gate level feature, wherein a position of the first gatecontact is offset in the first direction from either a position of thesecond gate contact or a position of the third gate contact or positionsof both the second and third gate contacts.
 13. An integrated circuit asrecited in claim 12, wherein the gate electrode level region includes agiven gate level feature that includes only one gate portion that formsa gate electrode of only one transistor of a given transistor type, thegiven gate level feature including an extension portion that extendsaway from its gate portion and over a non-diffusion region positionedbetween two diffusion regions of a diffusion type different than used toform the given transistor type.
 14. An integrated circuit as recited inclaim 13, wherein the first gate level feature has a first extensiondistance beyond a location at which the first gate contact physicallycontacts the first gate level feature, wherein the second gate levelfeature has a second extension distance beyond a location at which thesecond gate contact physically contacts the second gate level feature,wherein the third gate level feature has a third extension distancebeyond a location at which the third gate contact physically contactsthe third gate level feature, and wherein at least two of the first,second, and third extension distances are different.
 15. An integratedcircuit as recited in claim 1, wherein the second gate level feature iselectrically connected to the third gate level feature through a firstelectrical connection that extends in part through at least twointerconnect levels formed above the gate electrode level region.
 16. Anintegrated circuit as recited in claim 15, wherein the gate electrodesof the first and second transistors of the first transistor type arepositioned according to a gate pitch defined as an equalcenter-to-center spacing measured in the second direction betweenadjacent gate electrodes, and wherein the gate electrodes of the firstand second transistors of the second transistor type are positionedaccording to the gate pitch.
 17. An integrated circuit as recited inclaim 16, wherein all gate electrodes within the gate electrode levelregion are positioned according to the gate pitch such that a distancemeasured in the second direction between first-direction-orientedcenterlines of any two gate electrodes within the gate electrode levelregion is substantially equal to an integer multiple of the gate pitch.18. An integrated circuit as recited in claim 17, wherein the shareddiffusion region of the first diffusion type is electrically connectedto the shared diffusion region of the second diffusion type through asecond electrical connection that extends in part through a singleinterconnect level formed above the gate electrode level region.
 19. Anintegrated circuit as recited in claim 17, wherein the shared diffusionregion of the first diffusion type is electrically connected to theshared diffusion region of the second diffusion type through a secondelectrical connection that extends through at least two interconnectlevels formed above the gate electrode level region.
 20. An integratedcircuit as recited in claim 17, further comprising: a first gate contactdefined to physically contact the first gate level feature; a secondgate contact defined to physically contact the second gate levelfeature; and a third gate contact defined to physically contact thethird gate level feature, wherein a position of the first gate contactis offset in the first direction from either a position of the secondgate contact or a position of the third gate contact or positions ofboth the second and third gate contacts.
 21. An integrated circuit asrecited in claim 20, wherein the gate electrode level region includes agiven gate level feature that includes only one gate portion that formsa gate electrode of only one transistor of a given transistor type, thegiven gate level feature including an extension portion that extendsaway from its gate portion and over a non-diffusion region positionedbetween two diffusion regions of a diffusion type different than used toform the given transistor type.
 22. An integrated circuit as recited inclaim 21, wherein the first gate level feature has a first extensiondistance beyond a location at which the first gate contact physicallycontacts the first gate level feature, wherein the second gate levelfeature has a second extension distance beyond a location at which thesecond gate contact physically contacts the second gate level feature,wherein the third gate level feature has a third extension distancebeyond a location at which the third gate contact physically contactsthe third gate level feature, and wherein at least two of the first,second, and third extension distances are different.
 23. A method forcreating a layout of an integrated circuit, comprising: operating acomputer to define a gate electrode level region having a number ofadjacently positioned gate level feature layout channels, each gatelevel feature layout channel extending lengthwise in a first directionand widthwise in a second direction perpendicular to the firstdirection, wherein each of the number of adjacently positioned gatelevel feature layout channels includes at least one gate level feature,each gate level feature having a first end located adjacent to a lineend spacing and a second end located adjacent to another line endspacing, each gate level feature forming an electrically conductive pathextending between its first and second ends, wherein the gate electrodelevel region includes a first gate level feature that includes a firstpart that forms a gate electrode of a first transistor of a firsttransistor type and a second part that forms a gate electrode of a firsttransistor of a second transistor type, wherein the gate electrode ofthe first transistor of the first transistor type is substantiallyco-aligned with the gate electrode of the first transistor of the secondtransistor type along a first common line of extent in the firstdirection, and wherein the gate electrode of the first transistor of thefirst transistor type is electrically connected to the gate electrode ofthe first transistor of the second transistor type through the firstgate level feature, wherein the gate electrode level region includes asecond gate level feature that forms a gate electrode of a secondtransistor of the first transistor type, wherein the gate electrodelevel region includes a third gate level feature that forms a gateelectrode of a second transistor of the second transistor type, whereinthe second and third gate level features are located in different gatelevel feature layout channels, wherein gate electrode of the secondtransistor of the first transistor type is electrically connected to thegate electrode of the second transistor of the second transistor type,wherein the first and second transistors of the first transistor typeare collectively separated from the first and second transistors of thesecond transistor type by an inner portion of the gate electrode levelregion, wherein each of the first and second transistors of the firsttransistor type is formed in part by a shared diffusion region of afirst diffusion type located on a first side of the first gate levelfeature, wherein each of the first and second transistors of the secondtransistor type is formed in part by a shared diffusion region of asecond diffusion type located on a second side of the first gate levelfeature, and wherein the first and second sides of the first gate levelfeature are opposite sides of the first gate level feature.
 24. A datastorage device having program instructions stored thereon for generatinga layout of an integrated circuit, comprising: program instructions fordefining a gate electrode level region having a number of adjacentlypositioned gate level feature layout channels, each gate level featurelayout channel extending lengthwise in a first direction and widthwisein a second direction perpendicular to the first direction, wherein eachof the number of adjacently positioned gate level feature layoutchannels includes at least one gate level feature, each gate levelfeature having a first end located adjacent to a line end spacing and asecond end located adjacent to another line end spacing, each gate levelfeature forming an electrically conductive path extending between itsfirst and second ends, wherein the gate electrode level region includesa first gate level feature that includes a first part that forms a gateelectrode of a first transistor of a first transistor type and a secondpart that forms a gate electrode of a first transistor of a secondtransistor type, wherein the gate electrode of the first transistor ofthe first transistor type is substantially co-aligned with the gateelectrode of the first transistor of the second transistor type along afirst common line of extent in the first direction, and wherein the gateelectrode of the first transistor of the first transistor type iselectrically connected to the gate electrode of the first transistor ofthe second transistor type through the first gate level feature, whereinthe gate electrode level region includes a second gate level featurethat forms a gate electrode of a second transistor of the firsttransistor type, wherein the gate electrode level region includes athird gate level feature that forms a gate electrode of a secondtransistor of the second transistor type, wherein the second and thirdgate level features are located in different gate level feature layoutchannels, wherein gate electrode of the second transistor of the firsttransistor type is electrically connected to the gate electrode of thesecond transistor of the second transistor type, wherein the first andsecond transistors of the first transistor type are collectivelyseparated from the first and second transistors of the second transistortype by an inner portion of the gate electrode level region, whereineach of the first and second transistors of the first transistor type isformed in part by a shared diffusion region of a first diffusion typelocated on a first side of the first gate level feature, wherein each ofthe first and second transistors of the second transistor type is formedin part by a shared diffusion region of a second diffusion type locatedon a second side of the first gate level feature, and wherein the firstand second sides of the first gate level feature are opposite sides ofthe first gate level feature.